Method and system for cable modem initialization using dynamic servers

ABSTRACT

A method and system for initializing cable modems with dynamic protocol servers is provided. The method and system allow a dynamic protocol server such as a dynamic Trivial File Transfer Protocol (&#34;TFTP&#34;) server to override a request for a standard configuration file whose name is supplied to a cable modem in a Dynamic Host Configuration Protocol (&#34;DHCP&#34;) response message during initialization. Instead, the dynamic TFTP server identifies a cable modem by performing a reverse Domain Name System lookup of an Internet Protocol address used for the cable modem. Based on the determined identity for the cable modem, the dynamic TFTP server constructs a new configuration file specifically for the cable modem and transfers it to the cable modem. The new configuration file is different from the default configuration file originally requested by the cable modem. Creating a new configuration file with a dynamic protocol server allows greater flexibility for configuring cable modems in a data-over-cable system.

FIELD OF INVENTION

The present invention relates to communications in computer networks.More specifically, it relates to a method and system for using a dynamicconfiguration server for cable modem configuration.

BACKGROUND OF THE INVENTION

Cable television networks such as those provided by Comcast CableCommunications, Inc., of Philadelphia, Pa., Cox Communications ofAtlanta, Ga., Tele-Communications, Inc., of Englewood, Colo.,Time-Warner Cable, of Marietta, Ga., Continental Cablevision, Inc., ofBoston, Mass., and others provide cable television services to a largenumber of subscribers over a large geographical area. The cabletelevision networks typically are interconnected by cables such ascoaxial cables or a Hybrid Fiber/Coaxial ("HFC") cable system which havedata rates of about 10 Mega-bits-per-second ("Mbps") to 30+ Mbps.

The Internet, a world-wide-network of interconnected computers, providesmulti-media content including audio, video, graphics and text thattypically requires a large bandwidth for downloading and viewing. MostInternet Service Providers ("ISPs") allow customers to connect to theInternet via a serial telephone line from a Public Switched TelephoneNetwork ("PSTN") at data rates including 14,400 bps, 28,800 bps, 33,600bps, 56,000 bps and others that are much slower than the about 10 Mbpsto 30+ Mbps available on a coxial cable or HFC cable system on a cabletelevision network.

With the explosive growth of the Internet, many customers have desiredto use the larger bandwidth of a cable television network to connect tothe Internet and other computer networks. Cable modems, such as thoseprovided by 3Com Corporation of Santa Clara, Calif., U.S. RoboticsCorporation of Skokie, Ill., and others offer customers higher-speedconnectivity to the Internet, an intranet, Local Area Networks ("LANs")and other computer networks via cable television networks. These cablemodems currently support a data connection to the Internet and othercomputer networks via a cable television network with a "downstream"data rate of 30+ Mbps, which is a much larger data rate than can besupported by serial telephone line used over a modem.

However, most cable television networks provide only uni-directionalcable systems, supporting only a "downstream" data path. A downstreamdata path is the flow of data from a cable system "headend" to acustomer. A cable system headend is a central location in the cabletelevision network that is responsible for sending cable signals in thedownstream direction. A return data path via a telephone network, suchas a Public Switched Telephone Network provided by AT&T and others,(i.e., "telephony return") is typically used for an "upstream" datapath. An upstream data path is the flow of data from the customer backto the cable system headend. A cable television system with an upstreamconnection to a telephony network is called a "data-over-cable systemwith telephony return."

An exemplary data-over-cable system with telephony return includes acable modem termination system, a cable television network, a publicswitched telephone network, a telephony remote access concentrator, acable modem, customer premise equipment (e.g., a customer computer) anda data network (e.g., the Internet). The cable modem termination systemand the telephony remote access concentrator together are called a"telephony return termination system."

The cable modem termination system receives data packets from the datanetwork and transmits them downstream via the cable television networkto a cable modem attached to the customer premise equipment. Thecustomer premise equipment sends responses data packets to the cablemodem, which sends response data packets upstream via the publicswitched telephone network to the telephony remote access concentrator,which sends the response data packets back to the appropriate host onthe data network. The data-over-cable system with telephony returnprovides transparent Internet Protocol ("IP") data traffic betweencustomer premise equipment, a cable modem and the data network (e.g.,the Internet or an intranet). As is known in the art, IP is a routingprotocol designed to route traffic within a network or between networks.

When a cable modem used in the data-over-cable system with telephonyreturn is initialized, it will make a connection to both the cable modemtermination system via the cable network and to the telephony remoteaccess concentrator via the public switched telephone network. If thecable modem is using telephony return, it will acquire telephonyconnection parameters on a downstream connection from the cable modemtermination system and establish a Point-to-Point Protocol ("PPP")connection to connect an upstream channel to the telephony remote accessconcentrator. As is known in the art, PPP is used to encapsulatedatagrams over a serial communications link. After a PPP connection isestablished, the cable modem negotiates a telephony IP address with thetelephony remote access concentrator. The telephony IP address allowsthe customer premise equipment to send IP data packets upstream to thetelephony remote access concentrator via the public switched telephonenetwork to the data network.

The cable modem also makes an IP connection to the cable modemtermination system so that IP data received on the cable modemtermination system from the data network can be forwarded downstream tothe customer premise equipment via the cable network and the cablemodem.

Once an IP address is obtained on the cable modem termination system,the cable modem obtains the name of a configuration file used tocomplete initialization. The cable modem downloads a configuration filefrom a central location in the data-over-cable system using a TrivialFile Transfer Protocol ("TFTP") server. As is known in the art, TFTP isa very simple protocol used to transfer files, where any error duringfile transfer typically causes a termination of the file transfer.

There are several problems associated with using a configuration filefrom a central location to configure a cable modem. In a typical cablemodem initialization scenario, a Dynamic Host Configuration Protocol("DHCP") is used to obtain an IP address and to obtain the name of aconfiguration file on a DHCP server from which configuration parametersare obtained for cable modem initialization. The configuration file isdownloaded to the cable modem with TFTP using a TFTP server. Each DHCPserver has an identical copy of the same configuration file. Thus, eachcable modem in the data-over-cable system is configured exactly the sameway with the same configuration file with TFTP.

Since all cable modems in the data-over-cable are not made by the samemanufacturer and may be used for a number of different purposes, asingle common configuration file is inappropriate for all cable modemsin the data-over-cable system. However, if more than one configurationfile name is used in a data-over-cable system, DHCP servers would berequired to maintain a listing of configuration files for multiple cablemodem types. This would not be practical in a data-over-cable system. Inaddition, modifying DHCP servers to use more than one configuration fileviolates the spirit of the DHCP standard and is expensive since a largenumber of DHCP servers, including third-party DHCP servers in thedata-over-cable system would require modifications.

It is desirable to allow an individual cable modem to use configurationinformation from a configuration file different from the defaultconfiguration file without modifying existing DHCP servers or the DHCPinitialization process used to obtain an IP address and a configurationfile name.

SUMMARY OF THE INVENTION

In accordance with an illustrative embodiment of the present invention,the problems associated initializing a cable modem with configurationparameters from a common configuration file are overcome. A method andsystem is provided for initializing a cable modem with a configurationfile different from a common default configuration file.

The method includes receiving a first message on a first protocol serverfrom a network device including a name for a first configuration file toconfigure the network device. The name for the first configuration filewas obtained by the network device from a second protocol server using asecond protocol during an initialization sequence. An identity for thenetwork device is determined using one or more fields from the firstmessage. A second configuration file is constructed with multipleconfiguration parameters based on a determined identity for the networkdevice. The second configuration file is transferred to the networkdevice from the first protocol server using a first protocol in responseto the request in first message for the first configuration file. Thus,the network device receives a second configuration file different fromthe requested first configuration file.

In an illustrative embodiment of the present invention, a TFTP serverconnected to a cable modem termination system receives a TFTPRead-ReQuest ("RRQ") message from a cable modem in a data-over-cablesystem. The TFTP RRQ message includes a message field including a namefor a default configuration file sent to the cable modem by a DHCPserver in a DHCP response message during an initialization sequence. TheTFTP server extracts an IP address (e.g., 124.35.14.58) for the cablemodem which is included as part of a message header in the TFTP RRQmessage. The TFTP server performs a reverse look-up on the cable modem'sIP address through a Domain Name System ("DNS") using a reverse DNS namespace, also called the "in-addr.arpa" name space. Reverse DNS mappingmaps the IP address 124.35.14.58 back to a domain name for the cablemodem (e.g., "cm-type1.data-over-cable.net"). As is known in the art, adomain name is an English translation of a computer network address suchas an IP address.

The TFTP server determines what type of configuration parameters thecable modem requires by looking up the domain name determined for thecable modem in a table. The TFTP server constructs a secondconfiguration file with required configuration parameters, and any ofoptional configuration parameters or vendor specific configurationparameters for the cable modem based on its domain name. The secondconfiguration file constructed specifically for the cable modem istransferred to the cable modem from the TFTP server using the TFTPprotocol even though the cable modem requested a first configurationfile (i.e., a default configuration file) in the TFTP RRQ message.However, the present invention is not limited to the network devices,protocol servers and configuration files described above, and othernetwork devices, protocol servers and configuration file could also beused.

An illustrative embodiment of the present invention allows a TFTPserver, called a "dynamic TFTP server," to provide a configuration fileto an individual cable modem different than a common defaultconfiguration file requested by the cable modem. The dynamic TFTP serverconstructs a configuration file specifically for a cable modem based ona domain name for a cable modem and ignores a request for a defaultconfiguration file supplied to the cable modem during the DHCPinitialization sequence. Cable modems receive a configuration filedifferent from the default configuration file supplied by a DCHP serverwithout modifications to any DCHP servers or the DHCP initializationprocess. This provides flexibility for initialization of cable modems ina data-over-cable system. An illustrative embodiment of the presentinvention is described with respect to dynamic TFTP server. However,other dynamic servers may also be used and the present invention is notlimited to dynamic TFTP servers.

The foregoing and other features and advantages of an illustrativeembodiment of the present invention will be more readily apparent fromthe following detailed description, which proceeds with references tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a cable modem system withtelephony return;

FIG. 2 is a block diagram illustrating a protocol stack for a cablemodem;

FIG. 3 is a block diagram illustrating a Telephony Channel Descriptormessage structure;

FIG. 4 is a block diagram illustrating a Termination System Informationmessage structure;

FIG. 5 is a flow diagram illustrating a method for addressing hosts in acable modem system;

FIG. 6 is a block diagram illustrating a Dynamic Host ConfigurationProtocol message structure;

FIGS. 7A and 7B are a flow diagram illustrating a method for discoveringhosts in a cable modem system;

FIG. 8 is a block diagram illustrating a data-over-cable system for themethod illustrated in FIGS. 7A and 7B;

FIG. 9 is a block diagram illustrating the message flow of the methodillustrated in FIGS. 7A and 7B;

FIGS. 10A and 10B are a flow diagram illustrating a method for resolvinghost addresses in a data-over-cable system;

FIG. 11 is a flow diagram illustrating a method for resolving discoveredhost addresses; and

FIG. 12 is a block diagram illustrating the message flow of the methodillustrated in FIG. 10;

FIGS. 13A and 13B are a flow diagram illustrating a method for obtainingaddresses for customer premise equipment;

FIGS. 14A and 14B are a flow diagram illustrating a method for resolvingaddresses for customer premise equipment;

FIGS. 15A and 15B are a flow diagram illustrating a method foraddressing network host interfaces from customer premise equipment;

FIGS. 16A and 16B are a flow diagram illustrating a method for resolvingnetwork host interfaces from customer premise equipment;

FIG. 17 is a block diagram illustrating a message flow for the methodsin FIGS. 15A, 15B, and 16A and 16B;

FIG. 18 is a block diagram illustrating a data-over-cable system withdynamic protocol servers;

FIG. 19 is a flow diagram illustrating a method for obtaining aconfiguration file for a cable modem;

FIG. 20 is a flow diagram illustrating a method for obtaining aconfiguration file for a cable modem;

FIG. 21 is a block diagram illustrating a configuration file format fora cable modem; and

FIG. 22 is a flow diagram illustrating another method for obtaining aconfiguration file for a cable modem.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Cable Modem System with Telephony Return

FIG. 1 is a block diagram illustrating a data-over-cable system withtelephony return 10, hereinafter data-over-cable system 10. Most cableproviders known in the art predominately provide uni-directional cablesystems, supporting only a "downstream" data path. A downstream datapath is the flow of data from a cable television network "headend" tocustomer premise equipment (e.g., a customer's personal computer). Acable television network headend is a central location that isresponsible for sending cable signals in a downstream direction. Areturn path via a telephony network ("telephony return") is typicallyused for an "upstream" data path in uni-directional cable systems. Anupstream data path is the flow of data from customer premise equipmentback to the cable television network headend.

However, data-over-cable system 10 of the present invention may alsoprovide a bi-directional data path (i.e., both downstream and upstream)without telephony return as is also illustrated in FIG. 1 and thepresent invention is not limited to a data-over-cable system withtelephony return. In a data-over cable system without telephony return,customer premise equipment or cable modem has an upstream connection tothe cable modem termination system via a cable television connection, awireless connection, a satellite connection, or a connection via othertechnologies to send data upstream to the cable modem terminationsystem.

Data-over-cable system 10 includes a Cable Modem Termination System("CMTS") 12 connected to a cable television network 14, hereinaftercable network 14. Cable network 14 includes cable television networkssuch as those provided by Comcast Cable Communications, Inc., ofPhiladelphia, Pa., Cox Communications, or Atlanta, Ga.,Tele-Communications, Inc., of Englewood, Colo., Time-Warner Cable, ofMarietta, Ga., Continental Cablevision, Inc., of Boston, Mass., andothers. Cable network 14 is connected to a Cable Modem ("CM") 16 with adownstream cable connection.

CM 16 is connected to Customer Premise Equipment ("CPE") 18 such as apersonal computer system via a Cable Modem-to-CPE Interface ("CMCI") 20.CM 16 is connected to a Public Switched Telephone Network ("PSTN") 22with an upstream telephony connection. PSTN 22 includes those publicswitched telephone networks provided by AT&T, Regional Bell OperatingCompanies (e.g., Ameritch, U.S. West, Bell Atlantic, Southern BellCommunications, Bell South, NYNEX, and Pacific Telesis Group), GTE, andothers. The upstream telephony connection is any of a standard telephoneline connection, Integrated Services Digital Network ("ISDN")connection, Asymmetric Digital Subscriber Line ("ADSL") connection, orother telephony connection. PSTN 22 is connected to a Telephony RemoteAccess Concentrator ("TRAC") 24. In a data-over cable system withouttelephony return, CM 16 has an upstream connection to CMTS 12 via acable television connection, a wireless connection, a satelliteconnection, or a connection via other technologies to send data upstreamoutside of the telephony return path. An upstream cable televisionconnection via cable network 14 is illustrated in FIG. 1.

FIG. 1 illustrates a telephony modem integral to CM 16. In anotherembodiment of the present invention, the telephony modem is a separatemodem unit external to CM 16 used specifically for connecting with PSTN22. A separate telephony modem includes a connection to CM 16 forexchanging data. CM 16 includes cable modems provided by the 3ComCorporation of Santa Clara, Calif., U.S. Robotics Corporation of Skokie,Ill., and others. In yet another embodiment of the present invention, CM16 includes functionality to connect only to cable network 14 andreceives downstream signals from cable network 14 and sends upstreamsignals to cable network 14 without telephony return. The presentinvention is not limited to cable modems used with telephony return.

CMTS 12 and TRAC 24 may be at a "headend" of cable system 10, or TRAC 24may be located elsewhere and have routing associations to CMTS 12. CMTS12 and TRAC 24 together are called a "Telephony Return TerminationSystem" ("TRTS") 26. TRTS 26 is illustrated by a dashed box in FIG. 1.CMTS 12 and TRAC 24 make up TRTS 26 whether or not they are located atthe headend of cable network 14, and TRAC 24 may in located in adifferent geographic location from CMTS 12. Content severs, operationsservers, administrative servers and maintenance servers used indata-over-cable system 10 (not shown in FIG. 1) may also be in differentlocations. Access points to data-over-cable system 10 are connected toone or more CMTS's 12 or cable headend access points. Suchconfigurations may be "one-to-one", "one-to-many," or "many-to-many,"and may be interconnected to other Local Area Networks ("LANs") or WideArea Networks ("WANs").

TRAC 24 is connected to a data network 28 (e.g., the Internet or anintranet) by a TRAC-Network System Interface 30 ("TRAC-NSI"). CMTS 12 isconnected to data network 28 by a CMTS-Network System Interface("CMTS-NSI") 32. The present invention is not limited to data-over-cablesystem 10 illustrated in FIG. 1, and more or fewer components,connections and interfaces could also be used.

Cable Modem Protocol Stack

FIG. 2 is a block diagram illustrating a protocol stack 36 for CM 16.FIG. 2 illustrates the downstream and upstream protocols used in CM 16.As is known in the art, the Open System Interconnection ("OSI") model isused to describe computer networks. The OSI model consists of sevenlayers including from lowest-to-highest, a physical, data-link, network,transport, session, presentation and application layer. The physicallayer transmits bits over a communication link. The data link layertransmits error free frames of data. The network layer transmits androutes data packets.

For downstream data transmission, CM 16 is connected to cable network 14in a physical layer 38 via a Radio Frequency ("RF") Interface 40. In anillustrative embodiment of the present invention, RF Interface 40 has anoperation frequency range of 50 Mega-Hertz ("MHz") to 1 Giga-Hertz("GHz") and a channel bandwidth of 6 MHz. However, other operationfrequencies may also be used and the invention is not limited to thesefrequencies. RF interface 40 uses a signal modulation method ofQuadrature Amplitude Modulation ("QAM"). As is known in the art, QAM isused as a means of encoding digital information over radio, wire, orfiber optic transmission links. QAM is a combination of amplitude andphase modulation and is an extension of multiphase phase-shift-keying.QAM can have any number of discrete digital levels typically including4, 16, 64 or 256 levels. In one embodiment of the present invention,QAM-64 is used in RF interface 40. However, other operating frequenciesmodulation methods could also be used. For more information on RFinterface 40 see the Institute of Electrical and Electronic Engineers("IEEE") standard 802.14 for cable modems incorporated herein byreference. IEEE standards can be found on the World Wide Web at theUniversal Resource Locator ("URL") "www.ieee.org." However, other RFinterfaces 40 could also be used and the present invention is notlimited to IEEE 802.14 (e.g., RF interfaces from Multimedia CableNetwork Systems ("MCNS") and other could also be used).

Above RF interface 40 in a data-link layer 42 is a Medium Access Control("MAC") layer 44. As is known in the art, MAC layer 44 controls accessto a transmission medium via physical layer 38. For more information onMAC layer protocol 44 see IEEE 802.14 for cable modems. However, otherMAC layer protocols 44 could also be used and the present invention isnot limited to IEEE 802.14 MAC layer protocols (e.g., MCNS MAC layerprotocols and others could also be used).

Above MAC layer 44 is an optional link security protocol stack 46. Linksecurity protocol stack 46 prevents authorized users from making a dataconnection from cable network 14. RF interface 40 and MAC layer 44 canalso be used for an upstream connection if data-over-cable system 10 isused without telephony return.

For upstream data transmission with telephony return, CM 16 is connectedto PSTN 22 in physical layer 38 via modem interface 48. TheInternational Telecommunications Union-Telecommunication StandardizationSector ("ITU-T", formerly known as the CCITT) defines standards forcommunication devices identified by "V.xx" series where "xx" is anidentifying number. ITU-T standards can be found on the World Wide Webat the URL "www.itu.ch."

In one embodiment of the present invention, ITU-T V.34 is used as modeminterface 48. As is known in the art, ITU-T V.34 is commonly used in thedata link layer for modem communications and currently allows data ratesas high as 33,600 bits-per-second ("bps"). For more information see theITU-T V.34 standard. However, other modem interfaces or other telephonyinterfaces could also be used.

Above modem interface 48 in data link layer 42 is Point-to-PointProtocol ("PPP") layer 50, hereinafter PPP 50. As is known in the art,PPP is used to encapsulate network layer datagrams over a serialcommunications link. For more information on PPP see InternetEngineering Task Force ("IETF") Request for Comments ("RFC"), RFC-1661,RFC-1662 and RFC-1663 incorporated herein by reference. Information forIETF RFCs can be found on the World Wide Web at URLs "ds.internic.net"or "www.ietf.org."

Above both the downstream and upstream protocol layers in a networklayer 52 is an Internet Protocol ("IP") layer 54. IP layer 54,hereinafter IP 54, roughly corresponds to OSI layer 3, the networklayer, but is typically not defined as part of the OSI model. As isknown in the art, IP 54 is a routing protocol designed to route trafficwithin a network or between networks. For more information on IP 54 seeRFC-791 incorporated herein by reference.

Internet Control Message Protocol ("ICMP") layer 56 is used for networkmanagement. The main functions of ICMP layer 56, hereinafter ICMP 56,include error reporting, reachability testing (e.g., "pinging")congestion control, route-change notification, performance, subnetaddressing and others. Since IP 54 is an unacknowledged protocol,datagrams may be discarded and ICMP 56 is used for error reporting. Formore information on ICMP 56 see RFC-792 incorporated herein byreference.

Above IP 54 and ICMP 56 is a transport layer 58 with User DatagramProtocol layer 60 ("UDP"). UDP layer 60, hereinafter UDP 60, roughlycorresponds to OSI layer 4, the transport layer, but is typically notdefined as part of the OSI model. As is known in the art, UDP 60provides a connectionless mode of communications with datagrams. Formore information on UDP 60 see RFC-768 incorporated herein by reference.

Above the network layer are a Simple Network Management Protocol("SNMP") layer 62, Trivial File Protocol ("TFTP") layer 64, Dynamic HostConfiguration Protocol ("DHCP") layer 66 and a UDP manager 68. SNMPlayer 62 is used to support network management functions. For moreinformation on SNMP layer 62 see RFC-1157 incorporated herein byreference. TFTP layer 64 is a file transfer protocol used to downloadfiles and configuration information. For more information on TFTP layer64 see RFC-1350 incorporated herein by reference. DHCP layer 66 is aprotocol for passing configuration information to hosts on an IP 54network. For more information on DHCP layer 66 see RFC-1541 incorporatedherein by reference. UDP manager 68 distinguishes and routes packets toan appropriate service (e.g., a virtual tunnel). More or few protocollayers could also be used with data-over-cable system 10.

CM 16 supports transmission and reception of IP 54 datagrams asspecified by RFC-791. CMTS 12 and TRAC 24 may perform filtering of IP 54datagrams. CM 16 is configurable for IP 54 datagram filtering torestrict CM 16 and CPE 18 to the use of only their assigned IP 54addresses. CM 16 is configurable for IP 54 datagram UDP 60 portfiltering (i.e., deep filtering).

CM 16 forwards IP 54 datagrams destined to an IP 54 unicast addressacross cable network 14 or PSTN 22. Some routers have security featuresintended to filter out invalid users who alter or masquerade packets asif sent from a valid user. Since routing policy is under the control ofnetwork operators, such filtering is a vendor specific implementation.For example, dedicated interfaces (i.e., Frame Relay) may exist betweenTRAC 24 and CMTS 12 which preclude filtering, or various forms ofvirtual tunneling and reverse virtual tunneling could be used tovirtually source upstream packets from CM 16. For more information onvirtual tunneling see Level 2 Tunneling Protocol ("L2TP") orPoint-to-Point Tunneling Protocol ("PPTP") in IETF draft documentsincorporated herein by reference by Kory Hamzeh, et. al (IETF draftdocuments are precursors to IETF RFCs and are works in progress).

CM 16 also forwards IP 54 datagrams destined to an IP 54 multicastaddress across cable network 14 or PSTN 22. CM 16 is configurable tokeep IP 54 multicast routing tables and to use group membershipprotocols. CM 16 is also capable of IP 54 tunneling upstream through thetelephony path. A CM 16 that wants to send a multicast packet across avirtual tunnel will prepend another IP 54 header, set the destinationaddress in the new header to be the unicast address of CMTS 12 at theother end of the tunnel, and set the IP 54 protocol field to be four,which means the next protocol is IP 54.

CMTS 12 at the other end of the virtual tunnel receives the packet,strips off the encapsulating IP 54 header, and forwards the packet asappropriate. A broadcast IP 54 capability is dependent upon theconfiguration of the direct linkage, if any, between TRAC 24 and CMTS12. CMTS 12, CM 16, and TRAC 24 are capable of routing IP 54 datagramsdestined to an IP 54 broadcast address which is across cable network 14or PSTN 22 if so configured. CM 16 is configurable for IP 54 broadcastdatagram filtering.

An operating environment for the present invention includes a processingsystem with at least one high speed Central Processing Unit ("CPU") anda memory system. In accordance with the practices of persons skilled inthe art of computer programming, the present invention is describedbelow with reference to acts and symbolic representations of operationsthat are performed by the processing system, unless indicated otherwise.Such acts and operations are sometimes referred to as being"computer-executed", or "CPU executed."

It will be appreciated that the acts and symbolically representedoperations include the manipulation of electrical signals by the CPU.The electrical system represent data bits which cause a resultingtransformation or reduction of the electrical signal representation, andthe maintenance of data bits at memory locations in the memory system tothereby reconfigure or otherwise alter the CPU's operation, as well asother processing of signals. The memory locations where data bits aremaintained are physical locations that have particular electrical,magnetic, optical, or organic properties corresponding to the data bits.

The data bits may also be maintained on a computer readable mediumincluding magnetic disks, optical disks, organic disks, and any othervolatile or non-volatile mass storage system readable by the CPU. Thecomputer readable medium includes cooperating or interconnected computerreadable media, which exist exclusively on the processing system or isdistributed among multiple interconnected processing systems that may belocal or remote to the processing system.

Initialization of a Cable Modem with Telephony Return

When CM 16 is initially powered on, if telephony return is being used,CM 16 will receive a Telephony Channel Descriptor ("TCD") from CMTS 12that is used to provide dialing and access instructions on downstreamchannels via cable network 14. Information in the TCD is used by CM 16to connect to TRAC 24. The TCD is transmitted as a MAC managementmessage with a management type value of TRI₋₋ TCD at a periodic interval(e.g., every 2 seconds). To provide for flexibility, the TCD messageparameters are encoded in a Type/Length/Value ("TLV") form. However,other encoding techniques could also be used. FIG. 3 is a block diagramillustrating a TCD message structure 70 with MAC 44 management header 72and Service Provider Descriptor(s) ("SPD") 74 encoded in TLV format.SPDs 74 are compound TLV encodings that define telephony physical-layercharacteristics that are used by CM 16 to initiate a telephone call. SPD74 is a TLV-encoded data structure that contains sets of dialing andaccess parameters for CM 16 with telephony return. SPD 74 is containedwithin TCD message 70. There may be multiple SPD 74 encodings within asingle TCD message 70. There is at least one SPD 74 in TCD message 70.SPD 74 parameters are encoded as SPD-TLV tuples. SPD 74 contains theparameters shown in Table 1 and may contain optional vendor specificparameters. However, more or fewer parameters could also be used in SPD74.

                  TABLE 1                                                         ______________________________________                                        SPD 74 Parameter                                                                            Description                                                     ______________________________________                                        Factory Default Flag                                                                        Boolean value, if TRUE(1), indicates a                                        SPD which should be used by CM 16.                              Service Provider Name                                                                       This parameter includes the name of a                                         service provider. Format is standard                                          ASCII string composed of numbers and                                          letters.                                                        Telephone Numbers                                                                           These parameters contain telephone                                            numbers that CM 16 uses to initiate a                                         telephony modem link during a login                                           process. Connections are attempted in                                         ascending numeric order (i.e., Phone                                          Number 1, Phone Number 2...). The SPD                                         contains a valid telephony dial string as                                     the primary dial string (Phone Number 1),                                     secondary dial-strings are optional.                                          Format is ASCII string(s) composed of:                                        any sequence of numbers, pound "#" and                                        star "*" keys and comma character ","                                         used to indicate a two second pause in                                        dialing.                                                        Connection Threshold                                                                        The number of sequential connection                                           failures before indicating connection                                         failure. A dial attempt that does not result                                  in an answer and connection after no                                          more than ten rings is considered a                                           failure. The default value is one.                              Login User Name                                                                             This contains a user name CM 16 will use                                      an authentication protocol over the                                           telephone link during the initialization                                      procedure. Format is a monolithic                                             sequence of alphanumeric characters in                                        an ASCII string composed of numbers                                           and letters.                                                    Login Password                                                                              This contains a password that CM 16 will                                      use during authentication over a                                              telephone link during the initialization                                      procedure. Format is a monolithic                                             sequence of alphanumeric characters in                                        an ASCII string composed of numbers                                           and letters.                                                    DHCP Authenticate                                                                           Boolean value, reserved to indicate that                                      CM 16 uses a specific indicated DHCP 66                                       Server (see next parameter) for a DHCP                                        66 Client and BOOTP Relay Process                                             when TRUE (one). The default is FALSE                                         (zero) which allows any DHCP 66 Server.                         DHCP Server   IP 54 address value of a DHCP 66 Server                                       CM 16 uses for DHCP 66 Client and                                             BOOTP Relay Process. If this attribute is                                     present and DHCP 66 Authenticate                                              attribute is TRUE(1). The default value is                                    integer zero.                                                   RADIUS Realm  The realm name is a string that defines a                                     RADIUS server domain. Format is a                                             monolithic sequence of alphanumeric                                           characters in an ACSII string composed                                        of numbers and letters.                                         PPP Authentication                                                                          This parameter instructs the telephone                                        modem which authentication procedure to                                       perform over the telephone link.                                Demand Dial Timer                                                                           This parameter indicates time (in                                             seconds) of inactive networking time that                                     will be allowed to elapse before hanging                                      up a telephone connection at CM 16. If                                        this optional parameter is not present, or                                    set to zero, then the demand dial feature                                     is not activated. The default value is zero.                    Vendor Specific Extensions                                                                  Optional vendor specific extensions.                            ______________________________________                                    

A Termination System Information ("TSI") message is transmitted by CMTS12 at periodic intervals (e.g., every 2 seconds) to report CMTS 12information to CM 16 whether or not telephony return is used. The TSImessage is transmitted as a MAC 44 management message. The TSI providesa CMTS 12 boot record in a downstream channel to CM 16 via cable network14. Information in the TSI is used by CM 16 to obtain information aboutthe status of CMTS 12. The TSI message has a MAC 44 management typevalue of TRI₋₋ TSI.

FIG. 4 is a block diagram of a TSI message structure 76. TSI messagestructure 76 includes a MAC 44 management header 78, a downstreamchannel IP address 80, a registration IP address 82, a CMTS 12 boot time84, a downstream channel identifier 86, an epoch time 88 and vendorspecific TLV encoded data 90.

A description of the fields of TSI message 76 are shown in Table 2.However, more or fewer fields could also be used in TSI message 76.

                  TABLE 2                                                         ______________________________________                                        TSI 76 Parameter                                                                              Description                                                   ______________________________________                                        Downstream Channel                                                                            This field contains an IP 54 address of                       IP Address 80   CMTS 12 available on the downstream                                           channel this message arrived on.                              Registration IP Address 82                                                                    This field contains an IP 54 address                                          CM 16 sends its registration request                                          messages to. This address MAY be                                              the same as the Downstream Channel                                            IP 54 address.                                                CMTS Boot Time 84                                                                             Specifies an absolute-time of a CMTS                                          12 recorded epoch. The clock setting                                          for this epoch uses the current clock                                         time with an unspecified accuracy.                                            Time is represented as a 32 bit binary                                        number.                                                       Downstream Channel ID 86                                                                      A downstream channel on which this                                            message has been transmitted. This                                            identifier is arbitrarily chosen by CMTS                                      12 and is unique within the MAC 44                                            layer.                                                        Epoch 88        An integer value that is incremented                                          each time CMTS 12 is either re-                                               initialized or performs address or                                            routing table flush.                                          Vendor Specific Extensions 90                                                                 Optional vendor extensions may be                                             added as TLV encoded data.                                    ______________________________________                                    

After receiving TCD 70 message and TSI message 76, CM 16 continues toestablish access to data network 28 (and resources on the network) byfirst dialing into TRAC 24 and establishing a telephony PPP 50 session.Upon the completion of a successful PPP 50 connection, CM 16 performsPPP Link Control Protocol ("LCP") negotiation with TRAC 24. Once LCPnegotiation is complete, CM 16 requests Internet Protocol ControlProtocol ("IPCP") address negotiation. For more information on IPCP seeRFC-1332 incorporated herein by reference. During IPCP negotiation, CM16 negotiates an IP 54 address with TRAC 24 for sending IP 54 datapacket responses back to data network 28 via TRAC 24.

When CM 16 has established an IP 54 link to TRAC 24, it begins"upstream" communications to CMTS 12 via DHCP layer 66 to complete avirtual data connection by attempting to discover network hostinterfaces available on CMTS 12 (e.g., IP 54 host interfaces for avirtual IP 54 connection). The virtual data connection allows CM 16 toreceive data from data network 28 via CMTS 12 and cable network 14, andsend return data to data network 28 via TRAC 24 and PSTN 22. CM 16obtains an address from a host interface (e.g., an IP 54 interface)available on CMTS 12 that can be used by data network 28 to send data toCM 16. However, CM 16 has only a downstream connection from CMTS 12 andhas to obtain a connection address to data network 28 using an upstreamconnection to TRAC 24.

Addressing Network Host Interfaces in the Data-Over-Cable System Via theCable Modem

FIG. 5 is a flow diagram illustrating a method 92 for addressing networkhost interfaces in a data-over-cable system with telephony return via acable modem. Method 92 allows a cable modem to establish a virtual dataconnection to a data network. In method 92, multiple network devices areconnected to a first network with a downstream connection of a firstconnection type, and connected to a second network with an upstreamconnection of a second connection type. The first and second networksare connected to a third network with a third connection type.

At step 94, a selection input is received on a first network device fromthe first network over the downstream connection. The selection inputincludes a first connection address allowing the first network device tocommunicate with the first network via upstream connection to the secondnetwork. At step 96, a first message of a first type for a firstprotocol is created on the first network device having the firstconnection address from the selection input in a first message field.The first message is used to request a network host interface address onthe first network. The first connection address allows the first networkdevice to have the first message with the first message type forwardedto network host interfaces available on the first network via theupstream connection to the second network.

At step 98, the first network device sends the first message over theupstream connection to the second network. The second network uses thefirst address field in the first message to forward the first message toone or more network host interfaces available on first network at step100. Network host interfaces available on the first network that canprovide the services requested in first message send a second messagewith a second message type with a second connection address in a secondmessage field to the first network at step 102. The second connectionaddress allows the first network device to receive data packets from thethird network via a network host interface available on the firstnetwork. The first network forwards one or more second messages on thedownstream connection to the first network device at step 104.

The first network device selects a second connection address from one ofthe second messages from one of the one or more network host interfacesavailable on the first network at step 106 and establishes a virtualconnection from the third network to the first network device using thesecond connection address for the selected network host interface.

The virtual connection includes receiving data on the first network hostinterface on the first network from the third network and sending thedata over the downstream connection to the first network device. Thefirst network device sends data responses back to the third network overthe upstream connection to the second network, which forwards the datato the appropriate destination on the third network.

In one embodiment of the present invention, the data-over-cable systemis data-over-cable system 10, the first network device is CM 16, thefirst network is cable television network 14, the downstream connectionis a cable television connection. The second network is PSTN 22, theupstream connection is a telephony connection, the third network is datanetwork 28 (e.g., the Internet or an intranet) and the third type ofconnection is an IP 54 connection. The first and second connectionaddresses are IP 54 addresses. However, the present invention is notlimited to the network components and addresses described. Method 92allows CM 16 to determine an IP 54 network host interface addressavailable on CMTS 12 to receive IP 54 data packets from data network 28,thereby establishing a virtual IP 54 connection with data network 28.

After addressing network host interfaces using method 92, an exemplarydata path through cable system 10 is illustrated in Table 3. Howeverother data paths could also be used and the present invention is notlimited to the data paths shown in Table 3. For example, CM 16 may senddata upstream back through cable network 14 (e.g., CM 16 to cablenetwork 14 to CMTS 12) and not use PSTN 22 and the telephony returnupstream path.

                  TABLE 3                                                         ______________________________________                                        1.  An IP 54 datagram from data network 28 destined for CM 16 arrives             on CMTS-NSI 32 and enters CMTS 12.                                        2.  CMTS 12 encodes the IP 54 datagram in a cable data frame, passes it           to MAC 44 and transmits it "downstream" to RF interface 40 on                 CM 16 via cable network 14.                                               3.  CM 16 recognizes the encoded IP 54 datagram in MAC layer 44                   received via RF interface 40.                                             4.  CM 16 responds to the cable data frame and encapsulates a response            IP 54 datagram in a PPP 50 frame and transmits it "upstream" with             modem interface 48 via PSTN 22 to TRAC 24.                                5.  TRAC 24 decodes the IP 54 datagram and forwards it via TRAC-NSI               30 to a destination on data network 28.                                   ______________________________________                                    

Dynamic Network Host Configuration on Data-Over-Cable System

As was illustrated in FIG. 2, CM 16 includes a Dynamic HostConfiguration Protocol ("DHCP") layer 66, hereinafter DHCP 66. DHCP 66is used to provide configuration parameters to hosts on a network (e.g.,an IP 54 network). DHCP 66 consists of two components: a protocol fordelivering host-specific configuration parameters from a DHCP 66 serverto a host and a mechanism for allocation of network host addresses tohosts. DHCP 66 is built on a client-server model, where designated DHCP66 servers allocate network host addresses and deliver configurationparameters to dynamically configured network host clients.

FIG. 6 is a block diagram illustrating a DHCP 66 message structure 108.The format of DHCP 66 messages is based on the format of BOOTstrapProtocol ("BOOTP") messages described in RFC-951 and RFC-1542incorporated herein by reference. From a network host client's point ofview, DHCP 66 is an extension of the BOOTP mechanism. This behaviorallows existing BOOTP clients to interoperate with DHCP 66 serverswithout requiring any change to network host the clients' BOOTPinitialization software. DHCP 66 provides persistent storage of networkparameters for network host clients.

To capture BOOTP relay agent behavior described as part of the BOOTPspecification and to allow intcroperability of existing BOOTP clientswith DHCP 66 servers, DHCP 66 uses a BOOTP message format. Using BOOTPrelaying agents eliminates the necessity of having a DHCP 66 server oneach physical network segment.

DHCP 66 message structure 108 includes an operation code field 110("op"), a hardware address type field 112 ("htype"), a hardware addresslength field 114 ("hlen"), a number of hops field 116 ("hops"), atransaction identifier field 118 ("xid"), a seconds elapsed time field120 ("secs"), a flags field 122 ("flags"), a client IP address field 124("ciaddr"), a your IP address field 126 ("yiaddr"), a server IP addressfield 128 ("siaddr"), a gateway/relay agent IP address field 130("giaddr"), a client hardware address field 132 ("chaddr"), an optionalserver name field 134 ("sname"), a boot file name 136 ("file") and anoptional parameters field 138 ("options"). Descriptions for DHCP 66message 108 fields are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        DCHP 66                                                                       Parameter    Description                                                      ______________________________________                                        OP 110       Message op code / message type.                                               1 BOOTREQUEST, 2 = BOOTREPLY.                                    HTYPE 112    Hardware address type (e.g., `1` = 10                                         Mps Ethernet).                                                   HLEN 114     Hardware address length (e.g. `6` for 10                                      Mbps Ethernet).                                                  HOPS 116     Client sets to zero, optionally used by                                       relay-agents when booting via a relay-                                        agent.                                                           XID 118      Transaction ID, a random number                                               chosen by the client, used by the client                                      and server to associate messages and                                          responses between a client and a                                              server.                                                          SECS 120     Fitted in by client, seconds elapsed                                          since client started trying to boot.                             FLAGS 122    Flags including a BROADCAST bit.                                 CIADDR 124   Client IP address; filled in by client in                                     DHCPREQUEST if verifying previously                                           allocated configuration parameters.                              YIADDR 126   `Your`(client) IP address.                                       SIADDR 128   IP 54 address of next server to use in                                        bootstrap; returned in DHCPOFFER,                                             DHCPACK and DHCPNAK by server.                                   GIADDR 130   Gateway relay agent IP 54 address,                                            used in booting via a relay-agent.                               CHADDR       Client hardware address (e.g., MAC                               132          layer 44 address).                                               SNAME 134    Optional server host name, null                                               terminated string.                                               FILE 136     Boot file name, terminated by a null                                          string.                                                          OPTIONS      Optional parameters.                                             138                                                                           ______________________________________                                    

The DHCP 66 message structure shown in FIG. 6 is used to discover IP 54and other network host interfaces in data-over-cable system 10. Anetwork host client (e.g., CM 16) uses DHCP 66 to acquire or verify anIP 54 address and network parameters whenever the network parameters mayhave changed. Table 5 illustrates a typical use of the DHCP 66 protocolto discover a network host interface from a network host client.

                  TABLE 5                                                         ______________________________________                                        1.  A network host client broadcasts a DHCP DISCOVER 66 message                   on its local physical subnet. The DHCP DISCOVER 66 message may                include options that suggest values for a network host interface              address. BOOTP relay agents may pass the message on to DHCP 66                servers not on the same physical subnet.                                  2.  DHCP servers may respond with a DHCPOFFER message that                        includes an available network address in the `yiaddr` field (and              other                                                                         configuration parameters in DHCP 66 options) from a network host              interface. DHCP 66 servers unicasts the DHCPOFFER message to the              network host client (using the DHCP/BOOTP relay agent if                      necessary) if possible, or may broadcast the message to a broadcast           address (preferably 255.255.255.255) on the client's subnet.              3.  The network host client receives one or more DHCPOFFER messages               from one or more DHCP 66 servers. The network host client may                 choose to wait for multiple responses.                                    4.  The network host client chooses one DHCP 66 server with an                    associated network host interface from which to request                       configuration                                                                 parameters, based on the configuration parameters offered in the              DHCPOFFER messages.                                                       ______________________________________                                    

Discovering Network Host Interfaces in the Data-Over-Cable System

The DHCP discovery process illustrated in table 5 will not work indata-over-cable system 10. CM 16 has only a downstream connection fromCMTS 12, which includes DHCP 66 servers, associated with network hostinterfaces available on CMTS 12. In an illustrative embodiment of thepresent invention, CM 16 discovers network host interfaces via TRAC 24and PSTN 22 on an upstream connection.

The DHCP 66 addressing process shown in Table 5 was not originallyintended to discover network host interfaces in data-over-cable system10. CMTS 12 has DHCP 66 servers associated with network host interfaces(e.g., IP interfaces), but CM 16 only has as downstream connection fromCMTS 12. CM 16 has an upstream connection to TRAC 24, which has a DHCP66 layer. However, TRAC 24 does not have DHCP 66 servers, or directaccess to network host interfaces on CMTS 12.

FIGS. 7A and 7B are a flow diagram illustrating a method 140 fordiscovering network host interfaces in data-over-cable system 10. WhenCM 16 has established an IP 54 link to TRAC 24, it begins communicationswith CMTS 12 via DHCP 66 to complete a virtual IP 54 connection withdata network 28. However, to discover what IP 54 host interfaces mightbe available on CMTS 12, CM 16 has to communicate with CMTS 12 via PSTN22 and TRAC 24 since CM 16 only has a "downstream" cable channel fromCMTS 12.

At step 142 in FIG. 7A, after receiving a TSI message 76 from CMTS 12 ona downstream connection, CM 16 generates a DHCP discover("DHCPDISCOVER") message and sends it upstream via PSTN 22 to TRAC 22 todiscover what IP 54 interfaces are available on CMTS 12. The fields ofthe DHCP discover message are set as illustrated in Table 6. However,other field settings may also be used.

                  TABLE 6                                                         ______________________________________                                        DHCP 66                                                                       Parameter   Description                                                       ______________________________________                                        OP 110      Set to BOOTREQUEST.                                               HTYPE 112   Set to network type (e.g., one for 10 Mbps                                    Ethernet).                                                        HLEN 114    Set to network length (e.g., six for 10 Mbps                                  Ethernet)                                                         HOPS 116    Set to zero.                                                      FLAGS 118   Set BROADCAST bit to zero.                                        CIADDR 124  If CM 16 has previously been assigned an IP                                   54 address, the IP 54 address is placed in this                               field. If CM 16 has previously been assigned                                  an IP 54 address by DHCP 66, and also has                                     been assigned an address via IPCP, CM 16                                      places the DHCP 66 IP 54 address in this                                      field.                                                            GIADDR 130  CM 16 places the Downstream Channel IP 54                                     address 80 of CMTS 12 obtained in TSI                                         message 76 on a cable downstream channel                                      in this field.                                                    CHADDR 132  CM 16 places its 48-bit MAC 44 LAN address                                    in this field.                                                    ______________________________________                                    

The DHCPDISCOVER message is used to "discover" the existence of one ormore IP 54 host interfaces available on CMTS 12. DHCP 66 giaddr-field130 (FIG. 6) includes the downstream channel IP address 80 of CMTS 12obtained in TSI message 76 (e.g., the first message field from step 96of method 92). Using the downstream channel IP address 80 of CMTS 12obtained in TSI message 76 allows the DHCPDISCOVER message to beforwarded by TRAC 24 to DHCP 66 servers (i.e., protocol servers)associated with network host interfaces available on CMTS 12. If DHCP 66giaddr-field 130 (FIG. 6) in a DHCP message from a DHCP 66 client isnon-zero, the DHCP 66 server sends any return messages to a DHCP 66server port on a DHCP 66 relaying agent (e.g., CMTS 12) whose addressappears in DHCP 66 giaddr-field 130.

In a typical DHCP 66 discovery process the DHCP 66 giaddr-field 130 isset to zero. If DHCP 66 giaddr-field 130 is zero, the DHCP 66 client ison the same subnet as the DHCP 66 server, and the DHCP 66 server sendsany return messages to either the DHCP 66 client's network address, ifthat address was supplied in DHCP 66 ciaddr-field 124 (FIG. 6), or to aclient's hardware address specified in DHCP 66 chaddr-field 132 (FIG. 6)or to a local subnet broadcast address (e.g., 255.255.255.255).

At step 144, a DHCP 66 layer on TRAC 24 broadcasts the DHCPDISCOVERmessage on its local network leaving DHCP 66 giaddr-field 130 intactsince it already contains a non-zero value. TRAC's 24 local networkincludes connections to one or more DHCP 66 proxies (i.e., network hostinterface proxies). The DHCP 66 proxies accept DHCP 66 messagesoriginally from CM 16 destined for DHCP 66 servers connected to networkhost interfaces available on CMTS 12 since TRAC 24 has no direct accessto DCHP 66 servers associated with network host interfaces available onCMTS 12. DHCP 66 proxies are not used in a typical DHCP 66 discoveryprocess.

One or more DHCP 66 proxies on TRAC's 24 local network recognizes theDHCPDISCOVER message and forwards it to one or more DHCP 66 serversassociated with network host interfaces (e.g., IP 54 interfaces)available on CMTS 12 at step 146. Since DHCP 66 giaddr-field 130 (FIG.6) in the DHCPDISCOVER message sent by CM 16 is already non-zero (i.e.,contains the downstream IP address of CMTS 12), the DHCP 66 proxies alsoleave DHCP 66 giaddr-field 130 intact.

One or more DHCP 66 servers for network host interfaces (e.g., IP 54interfaces) available on CMTS 12 receive the DHCPDISCOVER message andgenerate a DHCP 66 offer message ("DHCPOFFER") at step 148. The DHCP 66offer message is an offer of configuration parameters sent from networkhost interfaces to DHCP 66 servers and back to a network host client(e.g., CM 16) in response to a DHCPDISCOVER message. The DHCP 66 offermessage is sent with the message fields set as illustrated in Table 7.However, other field settings can also be used. DHCP 66 yiaddr-field 126(e.g., second message field from step 102 of method 92) contains an IP54 address for a network host interface available on CMTS 12 and usedfor receiving data packets from data network 28.

                  TABLE 7                                                         ______________________________________                                        DHCP 66 Parameter                                                                              Description                                                  ______________________________________                                        FLAGS 122        BROADCAST bit set to zero.                                   YIADDR 126       IP 54 address from a network                                                  host interface to allow CM 16 to                                              receive data from data network                                                28 via a network host interface                                               available on CMTS 12.                                        SIADDR 128       An IP 54 address for a TFTP 64                                                server to download configuration                                              information for an interface host.                           CHADDR 132       MAC 44 address of CM 16.                                     SNAME 134        Optional DHCP 66 server                                                       identifier with an interface host.                           FILE 136         A TFTP 64 configuration file                                                  name for CM 16.                                              ______________________________________                                    

DHCP 66 servers send the DHCPOFFER message to the address specified in66 giaddr-field 130 (i.e., CMTS 12) from the DHCPDISCOVER message ifassociated network host interfaces (e.g., IP 54 interfaces) can offerthe requested service (e.g., IP 54 service) to CM 16. The DHCPDISOVERmessage DHCP 66 giaddr-field 130 contains a downstream channel IPaddress 80 of CMTS 12 that was received by CM 16 in TSI message 76. Thisallows CMTS 12 to receive the DHCPOFFER messages from the DHCP 66servers and send them to CM 16 via a downstream channel on cable network14.

At step 150 in FIG. 7B, CMTS 12 receives one or more DHCPOFFER messagesfrom one or more DHCP 66 servers associated with the network hostinterfaces (e.g., IP 54 interfaces). CMTS 12 examines DHCP 66yiaddr-field 126 and DHCP 66 chaddr-field 132 in the DHCPOFFER messagesand sends the DHCPOFFER messages to CM 16 via cable network 14. DHCP 66yiaddr-field 126 contains an IP 54 address for a network host IP 54interface available on CMTS 12 and used for receiving IP 54 data packetsfrom data network 28. DHCP 66 chaddr-field 132 contains the MAC 44 layeraddress for CM 16 on a downstream cable channel from CMTS 12 via cablenetwork 14. CMTS 12 knows the location of CM 16 since it sent CM 16 aMAC 44 layer address in one or more initialization messages (e.g., TSImessage 76).

If a BROADCAST bit in flags field 124 is set to one, CMTS 12 sends theDHCPOFFER messages to a broadcast IP 54 address (e.g., 255.255.255.255)instead of the address specified in DHCP 66 yiaddr-field 126. DHCP 66chaddr-field 132 is still used to determine that MAC 44 layer address.If the BROADCAST bit in DHCP 66 flags field 122 is set, CMTS 12 does notupdate internal address or routing tables based upon DHCP 66yiaddr-field 126 and DHCP 66 chaddr-field 132 pair when a broadcastmessage is sent.

At step 152, CM 16 receives one or more DHCPOFFER messages from CMTS 12via cable network 14 on a downstream connection. At step 154, CM 16selects an offer for IP 54 service from one of the network hostinterfaces (e.g., an IP interfaces 54) available on CMTS 12 thatresponded to the DHCPDISOVER message sent at step 142 in FIG. 7A andestablishes a virtual IP 54 connection. The selected DHCPOFFER messagecontains a network host interface address (e.g., IP 54 address) in DHCP66 yiaddr-field 126 (FIG. 6). A cable modem acknowledges the selectednetwork host interface with DHCP 66 message sequence explained below.

After selecting and acknowledging a network host interface, CM 16 hasdiscovered an IP 54 interface address available on CMTS 12 forcompleting a virtual IP 54 connection with data network 28.Acknowledging a network host interface is explained below. The virtualIP 54 connection allows IP 54 data from data network 28 to be sent toCMTS 12 which forwards the IP 54 packets to CM 16 on a downstreamchannel via cable network 14. CM 16 sends response IP 54 packets back todata network 28 via PSTN 22 and TRAC 24.

FIG. 8 is a block diagram illustrating a data-over-cable system 156 forthe method illustrated in FIGS. 7A and 7B. Data-over-cable system 156includes DHCP 66 proxies 158, DHCP 66 servers 160 and associated NetworkHost Interfaces 162 available on CMTS 12. Multiple DHCP 66 proxies 158,DHCP 66 servers 160 and network host interfaces 162 are illustrated assingle boxes in FIG. 8. FIG. 8 also illustrates DHCP 66 proxies 158separate from TRAC 24. In one embodiment of the present invention, TRAC24 includes DHCP 66 proxy functionality and no separate DHCP 66 proxies158 are used. In such an embodiment, TRAC 24 forwards DHCP 66 messagesusing DHCP 66 giaddr-field 130 to DHCP 66 servers 160 available on CMTS12. FIG. 9 is a block diagram illustrating a message flow 162 of method140 (FIGS. 7A and 7B).

Message flow 162 includes DHCP proxies 158 and DHCP servers 160illustrated in FIG. 8 Steps 142, 144, 146, 148, 150 and 154 of method140 (FIGS. 7A and 7B) are illustrated in FIG. 9. In one embodiment ofthe present invention, DHCP proxies 158 are not separate entities, butare included in TRAC 24. In such an embodiment, DHCP proxy services areprovided directly by TRAC 24.

Resolving Addresses for Network Host Interfaces

Since CM 16 receives multiple DHCPOFFER messages (Step 152 FIG. 7B) CM16 resolves and acknowledges one offer from a selected network hostinterface. FIGS. 10A and 10B are a flow diagram illustrating a method166 for resolving and acknowledging host addresses in a data-over-cablesystem. Method 166 includes a first network device that is connected toa first network with a downstream connection of a first connection type,and connected to a second network with an upstream connection of asecond connection type. The first and second networks are connected to athird network with a third connection type. In one embodiment of thepresent invention, the first network device is CM 16, the first networkis cable network 14, the second network is PSTN 22 and the third networkis data network 28 (e.g., the Internet). The downstream connection is acable television connection, the upstream connection is a telephonyconnection, and the third connection is an IP connection.

Turning to FIG. 10A, one or more first messages are received on thefirst network device from the first network on the downstream connectionat step 168. The one or more first messages are offers from one or morenetwork host interfaces available on the first network to provide thefirst network device a connection to the third network. The firstnetwork device selects one of the network host interfaces using messagefields in one of the one or more first messages at step 170. The firstnetwork device creates a second message with a second message type toaccept the offered services from a selected network host interface atstep 172. The second message includes a connection address for the firstnetwork in a first message field and an identifier to identify theselected network host interface in a second message field.

The first network device sends the second message over the upstreamconnection to the second network at step 174. The second network usesthe first message field in the second message to forward the secondmessage to the one or more network host interfaces available on firstnetwork at step 176.

A network host interface available on the first network identified insecond message field in the second message from the first network devicerecognizes an identifier for the network host interface at 178 in FIG.10B. The selected network host interface sends a third message with athird message type to the first network at step 180. The third messageis an acknowledgment for the first network device that the selectednetwork host interface received the second message from the firstnetwork device. The first network stores a connection address for theselected network interface in one or more tables on the first network atstep 182. The first network will forward data from the third network tothe first network device when it is received on the selected networkhost interface using the connection address in the one or more routingtables. The first network forwards the third message to the firstnetwork device on the downstream connection at step 184. The firstnetwork device receives the third message at step 186. The first networkand the first network device have the necessary addresses for a virtualconnection that allows data to be sent from the third network to anetwork host interface on the first network, and from the first networkover the downstream connection to the first network device. Method 166accomplishes resolving network interface hosts addresses from a cablemodem in a data-over-cable with telephony return.

Method 166 of the present invention is used in data-over-cable system 10with telephony return. However, the present invention is not limited todata-over-cable system 10 with telephony return and can be used indata-over-cable system 10 without telephony return by using an upstreamcable channel instead of an upstream telephony channel.

FIGS. 11A and 11B are a flow diagram illustrating a method 188 forresolving discovered host addresses in data-over-cable system 10 withtelephony return. At step 190 in FIG. 11A, CM 16 receives one or moreDHCPOFFER messages from one or more DHCP 66 servers associated with oneor more network host interfaces (e.g., at step 168 in method 166). Theone or more DHCPOFFER messages include DHCP 66 fields set as illustratedin Table 7 above. However, other field settings could also be used. Atstep 192, CM 16 selects one of the DHCPOFFER messages (see also, step170 in method 166). At step 194, CM 16 creates a DHCP 66 request message("DHCPREQUEST") message to request the services offered by a networkhost interface selected at step 192. The fields of the DHCP requestmessage are set as illustrated in Table 8. However, other field settingsmay also be used.

                  TABLE 8                                                         ______________________________________                                        DHCP 66                                                                       Parameter   Description                                                       ______________________________________                                        OP 110      Set to BOOTREQUEST.                                               HTYPE 112   Set to network type (e.g., one for 10Mbps                                     Ethernet).                                                        HLEN 114    Set to network length (e.g., six for 10Mbps                                   Ethernet)                                                         HOPS 116    Set to zero.                                                      FLAGS 118   Set BROADCAST bit to zero.                                        CIADDR 124  If CM 16 has previously been assigned an IP                                   address, the IP address is placed in this field.                              If CM 16 has previously been assigned an IP                                   address by DHCP 66, and also has been                                         assigned an address via IPCP, CM 16 places                                    the DHCP 66 IP 54 address in this field.                          YIADDR 126  IP 54 address sent from the selected network                                  interface host in DCHPOFFER message                               GIADDR 130  CM 16 places the Downstream Channel IP 54                                     address 80 CMTS 12 obtained in TSI                                            message 76 on a cable downstream channel                                      in this field.                                                    CHADDR 132  CM 16 places its 48-bit MAC 44 LAN address                                    in this field.                                                    SNAME 134   DHCP 66 server identifier for the selected                                    network interface host                                            ______________________________________                                    

The DHCPREQUEST message is used to "request" services from the selectedIP 54 host interface available on CMTS 12 using a DHCP 66 serverassociated with the selected network host interface. DHCP 66giaddr-field 130 (FIG. 6) includes the downstream channel IP address 80for CMTS 12 obtained in TSI message 76 (e.g., the first message-fieldfrom step 172 of method 166). Putting the downstream channel IP address80 obtained in TSI message 76 allows the DHCPREQUEST message to beforwarded by TRAC 24 to DCHP 66 servers associated with network hostinterfaces available on CMTS 12. DHCP 66 giaddr-field 126 contains anidentifier (second message field, step 172 in method 166) DHCP 66sname-field 134 contains a DHCP 66 server identifier associated with theselected network host interface.

If DHCP 66 giaddr-field 130 in a DHCP message from a DHCP 66 client isnon-zero, a DHCP 66 server sends any return messages to a DHCP 66 serverport on a DHCP 66 relaying agent (e.g., CMTS 12) whose address appearsin DHCP 66 giaddr-field 130. If DHCP 66 giaddr-field 130 is zero, theDHCP 66 client is on the same subnet as the DHCP 66 server, and the DHCP66 server sends any return messages to either the DHCP 66 client'snetwork address, if that address was supplied in DHCP 66 ciaddr-field124, or to the client's hardware address specified in DHCP 66chaddr-field 132 or to the local subnet broadcast address.

Returning to FIG. 11A at step 196, CM 16 sends the DHCPREQUEST messageon the upstream connection to TRAC 24 via PSTN 22. At step 198, a DHCP66 layer on TRAC 24 broadcasts the DHCPREQUEST message on its localnetwork leaving DHCP 66 giaddr-field 130 intact since it alreadycontains a non-zero value. TRAC's 24 local network includes connectionsto one or more DHCP 66 proxies. The DHCP 66 proxies accept DHCP 66messages originally from CM 16 destined for DHCP 66 servers associatedwith network host interfaces available on CMTS 12. In another embodimentof the present invention, TRAC 24 provides the DHCP 66 proxyfunctionality, and no separate DHCP 66 proxies are used.

The one or more DHCP 66 proxies on TRAC's 24 local network messageforwards the DHCPOFFER to one or more of the DHCP 66 servers associatedwith network host interfaces (e.g., IP 54 interfaces) available on CMTS12 at step 200 in FIG. 11B. Since DHCP 66 giaddr-field 130 in theDHCPDISCOVER message sent by CM 16 is already non-zero (i.e., containsthe downstream IP address of CMTS 12), the DHCP 66 proxies leave DHCP 66giaddr-field 130 intact.

One or more DHCP 66 servers for the selected network host interfaces(e.g., IP 54 interface) available on CMTS 12 receives the DHCPOFFERmessage at step 202. A selected DHCP 66 server recognizes a DHCP 66server identifier in DHCP 66 sname-field 134 or the IP 54 address thatwas sent in the DCHPOFFER message in the DHCP 66 yiaddr-field 126 fromthe DHCPREQUST message as being for the selected DHCP 66 server.

The selected DHCP 66 server associated with network host interfaceselected by CM 16 in the DHCPREQUEST message creates and sends a DCHP 66acknowledgment message ("DHCPACK") to CMTS 12 at step 204. The DHCPACKmessage is sent with the message fields set as illustrated in Table 9.However, other field settings can also be used. DHCP 66 yiaddr-fieldagain contains the IP 54 address for the selected network host interfaceavailable on CMTS 12 for receiving data packets from data network 28.

                  TABLE 9                                                         ______________________________________                                        DHCP 66 Parameter                                                                             Description                                                   ______________________________________                                        FLAGS 122       Set a BROADCAST bit to zero.                                  YIADDR 126      IP 54 address for the selected                                                network host interface to allow                                               CM 16 to receive data from data                                               network 28.                                                   SIADDR 128      An IP 54 address for a TFTP 64                                                server to download configuration                                              information for an interface host.                            CHADDR 132      MAC 44 address of CM 16.                                      SNAME 134       DHCP 66 server identifier                                                     associated with the selected                                                  network host interface.                                       FILE 136        A configuration file name for an                                              network interface host.                                       ______________________________________                                    

The selected DHCP 66 server sends the DHCACK message to the addressspecified in DHCP 66 giaddr-field 130 from the DHCPREQUEST message to CM16 to verify the selected network host interface (e.g., IP 54 interface)will offer the requested service (e.g., IP 54 service).

At step 206, CMTS 12 receives the DHCPACK message from the selected DHCP66 server associated with the selected network host interface IP 54address(e.g., IP 54 interface). CMTS 12 examines DHCP 66 yiaddr-field126 and DHCP 66 chaddr-field 132 in the DHCPOFFER messages. DHCP 66yiaddr-field 126 contains an IP 54 address for a network host IP 54interface available on CMTS 12 and used for receiving IP 54 data packetsfrom data network 28 for CM 16. DHCP 66 chaddr-field 132 contains theMAC 44 layer address for CM 16 on a downstream cable channel from CMTS12 via cable network 14.

CMTS 12 updates an Address Resolution Protocol ("ARP") table and otherrouting tables on CMTS 12 to reflect the addresses in DHCP 66yiaddr-field 126 and DHCP 66 chaddr-field 132 at step 208. As is knownin the art, ARP allows a gateway such as CMTS 12 to forward anydatagrams from a data network such as data network 28 it receives forhosts such as CM 16. ARP is defined in RFC-826, incorporated herein byreference. CMTS 12 stores a pair of network address values in the ARPtable, the IP 54 address of the selected network host interface fromDHCP 66 yiaddr-field 126 and a Network Point of Attachment ("NPA")address. In an illustrative embodiment of the present invention, The NPAaddress is a MAC 44 layer address for CM 16 via a downstream cablechannel. The IP/NPA address pair are stored in local routing tables withthe IP/NPA addresses of hosts (e.g., CMs 16) that are attached to cablenetwork 14.

At step 210, CMTS 12 sends the DHCPACK message to CM 16 via cablenetwork 14. At step 212, CM 16 receives the DHCPACK message, and alongwith CMTS 12 has addresses for a virtual connection between data network28 and CM 16. When data packets arrive on the IP 54 address for theselected host interface they are sent to CMTS 12 and CMTS 12 forwardsthem using a NPA (i.e., MAC 44 address) from the routing tables on adownstream channel via cable network 14 to CM 16.

If a BROADCAST bit in flags field 124 is set to one in the DHCPACK, CMTS12 sends the DHCPACK messages to a broadcast IP 54 address (e.g.,255.255.255.255). DHCP 66 chaddr-field 132 is still used to determinethat MAC layer address. If the BROADCAST bit in flags field 122 is set,CMTS 12 does not update the ARP table or offer routing tables based uponDHCP 66 yiaddr-field 126 and DHCP 66 chaddr-field 132 pair when abroadcast message is sent.

FIG. 12 is a block diagram illustrating the message flow 214 of themethod 188 illustrated in FIGS. 11A and 11B. Message flow 214 includesDHCP proxies 158 and DHCP servers 160 illustrated in FIG. 8. Methodsteps 194, 196, 198, 204, 208, 210and 212 of method 188 (FIGS. 11A and11B) are illustrated in FIG. 12. In one embodiment of the presentinvention, DHCP proxies 158 are not separate entities, but are includedin TRAC 24. In such an embodiment, DHCP proxy services are provideddirectly by TRAC 24.

After method 188, CMTS 12 has a valid IP/MAC address pair in one or moreaddress routing tables including an ARP table to forward IP 54 datapackets from data network 28 to CM 16, thereby creating a virtual IP 54data path to/from CM 16 as was illustrated in method 92 (FIG. 5) andTable 3. CM 16 has necessary parameters to proceed to the next phase ofinitialization, a download of a configuration file via TFTP 64. Once CM16 has received the configuration file and has been initialized, itregisters with CMTS 12 and is ready to receive data from data network14.

In the event that CM 16 is not compatible with the configuration of thenetwork host interface received in the DHCPACK message, CM 16 maygenerate a DHCP 66 decline message ("DHCPDECLINE") and transmit it toTRAC 24 via PSTN 22. A DHCP 66 layer in TRAC 24 forwards the DHCPDECLINEmessage to CMTS 12. Upon seeing a DHCPDECLINE message, CMTS 12 flushesits ARP tables and routing tables to remove the now invalid IP/MACpairing. If an IP 54 address for a network host interface is returnedthat is different from the IP 54 address sent by CM 16 in theDCHCPREQUEST message, CM 16 uses the IP 54 address it receives in theDHCPACK message as the IP 54 address of the selected network hostinterface for receiving data from data network 28.

The present invention is described with respect to, but is not limitedto a data-over-cable-system with telephony return. Method 188 can alsobe used with a cable modem that has a two-way connection (i.e., upstreamand downstream) to cable network 14 and CMTS 12. In adata-over-cable-system without telephony return, CM 16 would broadcastthe DHCPREQUEST message to one or more DHCP 66 servers associated withone or more network host interfaces available on CMTS 12 using anupstream connection on data network 14 including the IP 54 address ofCMTS 12 in DHCP 66 giaddr-field 130. Method 188 accomplishes resolvingaddresses for network interface hosts from a cable modem in adata-over-cable with or without telephony return, and without extensionsto the existing DHCP protocol.

CPE Initialization in a Data-Over-Cable System

CPE 18 also uses DHCP 66 to generate requests to obtain IP 54 addressesto allow CPE 18 to also receive data from data network 28 via CM 16. Inan illustrative embodiment of the present invention, CM 16 functions asa standard BOOTP relay agent/DHCP Proxy 158 to facilitate CPE's 18access to DHCP 66 server 160. FIGS. 13A and 13B are a flow diagramillustrating a method 216 for obtaining addresses for customer premiseequipment. CM 16 and CMTS 12 use information from method 214 toconstruct IP 54 routing and ARP table entries for network hostinterfaces 162 providing data to CMCI 20 and to CPE 18.

Method 216 in FIGS. 13A and 13B includes a data-over-cable system withtelephony return and first network device with a second network devicefor connecting the first network device to a first network with adownstream connection of a first connection type, and for connecting toa second network with an upstream connection of a second connectiontype. The first and second networks are connected to a third networkwith a third connection type.

In one embodiment of the present invention, data-over-cable system withtelephony return is data-over-cable system 10 with the first networkdevice CPE 18 and the second network device CM 16. The first network iscable television network 14, the downstream connection is a cabletelevision connection, the second network is PSTN 22, the upstreamconnection is a telephony connection, the third network is data network28 (e.g., the Internet or an intranet) and the third type of connectionis an IP 54 connection. However, the present invention is not limited tothe network components described and other network components may alsobe used. Method 216 allows CPE 18 to determine an IP 54 network hostinterface address available on CMTS 12 to receive IP 54 data packetsfrom data network 54, thereby establishing a virtual IP 54 connectionwith data network 28 via CM 16.

Returning to FIG. 13A at step 218, a first message of a first type(e.g., a DHCP 66 discover message) with a first message field for afirst connection is created on the first network device. The firstmessage is used to discover a network host interface address on thefirst network to allow a virtual connection to the third network.

At step 220, the first network device sends the first message to thesecond network device. The second network device checks the firstmessage field at step 222. If the first message field is zero, thesecond network device puts its own connection address into the firstmessage field at step 224. The second network device connection addressallows the messages from network host interfaces on the first network toreturn messages to the second network device attached to the firstnetwork device. If the first message field is non-zero, the secondnetwork device does not alter the first message field since there couldbe a relay agent attached to the first network device that may set thefirst connection address field.

At step 226, the second network device forwards the first message to aconnection address over the upstream connection to the second network.In one embodiment of the present invention, the connection address is anIP broadcast address (e.g., 255.255.255.255). However, other connectionaddresses can also be used.

The second network uses the first connection address in the firstmessage field in the first message to forward the first message to oneor more network host interfaces (e.g., IP 54 network host interfaces)available on first network at step 228. One or more network hostinterfaces available on the first network that can provide the servicesrequested in first message send a second message with a second messagetype with a second connection address in a second message field to thefirst network at step 230 in FIG. 13B. The second connection addressallows the first network device to receive data packets from the thirdnetwork via a network host interface on the first network. The firstnetwork forwards the one or more second messages on the downstreamconnection to the second network device at step 232. The second networkdevice forwards the one or more second messages to the first networkdevice at step 234. The first network device selects one of the one ormore network host interfaces on the first network using the one or moresecond messages at step 236. This allows a virtual connection to beestablished between the third network and the first network device viathe selected network host interface on the first network and the secondnetwork device.

FIGS. 14A and 14B are a flow diagram illustrating a method 240 forresolving addresses for the network host interface selected by a firstnetwork device to create a virtual connection to the third network.Turning to FIG. 14A, at step 240 one or more second messages arereceived with a second message type on the first network device from thesecond network device from the first network on a downstream connectionat step 242. The one or more second messages are offers from one or moreprotocol servers associated with one or more network host interfacesavailable on the first network to provide the first network device aconnection to the third network. The first network device selects one ofthe network host interfaces using one of the one or more second messagesat step 244. The first network device creates a third message with athird message type to accept the offered services from the selectednetwork host interface at step 246. The third message includes aconnection address for the first network in a first message field and anidentifier to identify the selected network host interface in a secondmessage field. At step 248, first network device equipment sends thethird message to the second network device.

The second network device sends the third message over the upstreamconnection to the second network at step 250. The second network usesthe first message field in the third message to forward the thirdmessage to the one or more network host interfaces available on firstnetwork at step 252.

A network host interface available on the first network identified insecond message field in the third message from the first network devicerecognizes an identifier for the selected network host interface at step254 in FIG. 14B. The selected network host interface sends a fourthmessage with a fourth message type to the first network at step 256. Thefourth message is an acknowledgment for the first network device thatthe selected network host interface received the third message. Thefourth message includes a second connection address in a third messagefield. The second connection address is a connection address for theselected network host interface. The first network stores the connectionaddress for the selected network interface from the third message in oneor more routing tables (e.g., an ARP table) on the first network at step258. The first network will forward data from the third network to thefirst network device via the second network device when it is receivedon the selected network host interface using the connection address fromthe third message field. The first network forwards the fourth messageto the second network device on the downstream connection at step 260.The second network device receives the fourth message and stores theconnection address from the third message field for the selected networkinterface in one or more routing tables on the second network device atstep 262. The connection address for the selected network interfaceallows the second network device to forward data from the third networksent by the selected network interface to the customer premiseequipment.

At step 264, the second network device forward the fourth message to thefirst network device. At step 266, the first network device establishesa virtual connection between the third network and the first networkdevice.

After step 266, the first network, the second network device and thefirst network device have the necessary connection addresses for avirtual connection that allows data to be sent from the third network toa network host interface on the first network, and from the firstnetwork over the downstream connection to the second network and then tothe first network device. In one embodiment of the present invention,method 240 accomplishes resolving network interface hosts addresses fromcustomer premise equipment with a cable modem in a data-over-cable withtelephony return without extensions to the existing DHCP protocol.

Methods 216 and 240 of the present invention are used in data-over-cablesystem 10 with telephony return with CM 16 and CPE 18. However, thepresent invention is not limited to data-over-cable system 10 withtelephony return and can be used in data-over-cable system 10 withouttelephony return by using an upstream cable channel instead of anupstream telephony channel.

FIGS. 15A and 15B are a flow diagram illustrating a method 268 foraddressing network host interfaces from CPE 18. At step 270 in FIG. 15A,CPE 18 generates a DHCPDISCOVER message broadcasts the DHCPDISCOVERmessage on its local network with the fields set as illustrated in Table6 above with addresses for CPE 18 instead of CM 16. However, more orfewer field could also be set. CM 16 receives the DHCPDISCOVER as astandard BOOTP relay agent at step 272. The DHCP DISCOVER message has aMAC 44 layer address for CPE 18 in DHCP 66 chaddr-field 132, which CM 16stores in one or more routing tables. As a BOOTP relay agent, the CM 16checks the DHCP 66 giaddr-field 130 (FIG. 6) at step 274. If DHCP 66giaddr-field 130 is set to zero, CM 16 put its IP 54 address into DHCP66 giaddr-field 130 at step 276.

If DHCP 66 giaddr-field 130 is non-zero, CM 16 does not alter DHCP 66giaddr-field 130 since there could be another BOOTP relay agent attachedto CPE 18 which may have already set DHCP 66 giaddr-field 130. Any BOOTPrelay agent attached to CPE 18 would have also have acquired its IP 54address from using a DCHP 66 discovery process (e.g., FIG. 12).

Returning to FIG. 15A, at step 278, CM 16 broadcasts the DHCPDISCOVERmessage to a broadcast address via PSTN 22 to TRAC 24. In one embodimentof the present invention, the broadcast address is an IP 54 broadcastaddress (e.g., 255.255.255.255). At step 280, one or more DHCP 66proxies 158 associated with TRAC 24, recognize the DHCPDISOVER message,and forward it to one or more DHCP 66 servers 160 associated with one ormore network host interfaces 162 available on CMTS 12. Since DHCP 66giaddr-field 130 is already non-zero, the DHCP proxies leave DHCP 66giaddr-field 130 intact. In another embodiment of the present invention,TRAC 24 includes DCHP 66 proxy 158 functionality and no separate DHCP 66proxies 158 are used.

At step 282 in FIG. 15B, the one or more DHCP servers 160 receive theDHCPDISCOVER message from one or more DHCP proxies, and generate one ormore DHCPOFFER messages to offer connection services for one or morenetwork host interfaces 162 available on CMTS 12 with the fields set asillustrated in Table 7. The one or more DHCP servers 160 send the one ormore DHCPOFFER messages to the address specified in DHCP 66 giaddr-field130 (e.g., CM 16 or a BOOTP relay agent on CPE 18), which is an IP 54address already contained in an ARP or other routing table in CMTS 12.Since CMTS 12 also functions as a relay agent for the one or more DHCPservers 160, the one or more DHCPOFFER messages are received on CMTS 12at step 284.

CMTS 12 examines DHCP 66 yiaddr-field 126 and DHCP 66 giaddr-field 130in the DHCPOFFER messages, and sends the DHCPOFFER messages down cablenetwork 14 to IP 54 address specified in the giaddr-field 130. The MAC44 address for CM 16 is obtained through a look-up of the hardwareaddress associated with DHCP 66 chaddr-field 130. If the BROADCAST bitin DHCP 66 flags-field 122 is set to one, CMTS 12 sends the DHCPOFFERmessage to a broadcast IP 54 address (e.g., 255.255.255.255), instead ofthe address specified in DHCP 66 yiaddr-field 126. CMTS 12 does notupdate its ARP or other routing tables based upon the broadcast DCHP 66yiaddr-field 126 DHCP 66 chaddr-field 132 address pair.

Returning to FIG. 15B, CM 16 reccives the one or more DHCPOFFER messagesand forwards them to CPE 18 at step 286. CM 16 uses the MAC 44 addressspecified determined by DHCP 66 chaddr-field 132 look-up in its routingtables to find the address of CPE 18 even if the BROADCAST bit in DHCP66 flags-field 122 is set. At step 290, CPE 18 receives the one or moreDHCPOFFER messages from CM 16. At step 292, CPE 18 selects one of theDHCPOFFER messages to allow a virtual connection to be establishedbetween data network 28 and CPE 18. Method 266 accomplishes addressingnetwork interface hosts from CPE 18 in data-over-cable system 10 withoutextensions to the existing DHCP protocol.

FIGS. 16A and 16B are a flow diagram illustrating a method 294 forresolving network host interfaces from CPE 18. At step 296, CPE 18receives the one or more DHCPOFFER messages from one or more DHCP 66servers associated with one or more network host interface available onCMTS 12. At step 298, CPE 18 chooses one offer of services from aselected network host interface. At step 300, CPE 18 generates aDHCPREQUEST message with the fields set as illustrated in Table 8 abovewith addresses for CPE 18 instead of CM 16. However, more or fewerfields could also be set. At step 302, CPE 18 sends the DHCPREQUESTmessage to CM 16. At step 304, CM 16 forwards the message to TRAC 24 viaPSTN 22.

At step 306, a DHCP 66 layer on TRAC 24 broadcasts the DHCPREQUESTmessage on its local network leaving DHCP 66 giaddr-field 130 intactsince it already contains a non-zero value. TRAC's 24 local networkincludes connections to one or more DHCP 66 proxies. The DHCP 66 proxiesaccept DHCP 66 messages originally from CPE 18 destined for DHCP 66servers associated with network host interfaces available on CMTS 12. Inanother embodiment of the present invention, TRAC 24 provides the DHCP66 proxy functionality, and no separate DHCP 66 proxies are used.

One or more DHCP 66 proxies on TRAC's 24 local network recognize theDHCPOFFER message and forward it to one or more of the DHCP 66 serversassociated with network host interfaces (e.g., IP 54 interfaces)available on CMTS 12 at step 308 in FIG. 16B. Since DHCP 66 giaddr-field130 in the DHCPDISCOVER message sent by CPE 18 is already non-zero, theDHCP 66 proxies leave DHCP 66 giaddr-field 130 intact.

One or more DHCP 66 servers for the selected network host interfaces(e.g., IP 54 interface) available on CMTS 12 receive the DHCPOFFERmessage at step 310. A selected DHCP 66 server recognizes a DHCP 66server identifier in DHCP 66 sname-field 134 or the IP 54 address thatwas sent in the DCHPOFFER message in the DHCP 66 yiaddr-field 126 fromthe DHCPREQUST message for the selected DHCP 66 server.

The selected DHCP 66 server associated with network host interfaceselected by CPE 18 in the DHCPREQUEST message creates and sends a DCHPacknowledgment message ("DHCPACK") to CMTS 12 at step 312 using the DHCP66 giaddr-field 130. The DHCPACK message is sent with the message fieldsset as illustrated in Table 9. However, other field settings can also beused. DHCP 66 yiaddr-field contains the IP 54 address for the selectednetwork host interface available on CMTS 12 for receiving data packetsfrom data network 28 for CPE 18.

At step 314, CMTS 12 receives the DHCPACK message. CMTS 12 examines theDHCP 66 giaddr-field 130 and looks up that IP address in its ARP tablefor an associated MAC 44 address. This is a MAC 44 address for CM 16,which sent the DHCPREQUEST message from CPE 18. CMTS 12 uses the MAC 44address associated with the DHCP 66 giaddr-field 130 and the DHCP 66yiaddr-field 126 to update its routing and ARP tables reflecting thisaddress pairing at step 316. At step 318, CMTS 12 sends the DHCPACKmessage on a downstream channel on cable network 14 to the IP 54 and MAC44 addresses, respectively (i.e., to CM 16). If the BROADCAST bit in theDHCP 66 flags-field 122 is set to one, CMTS 12 sends the DHCPACK messageto a broadcast IP 54 address (e.g., 255.255.255.255), instead of theaddress specified in the DHCP 66 yiaddr-field 126. CMTS 12 uses the MAC44 address associated with the DHCP 66 chaddr-field 130 even if theBROADCAST bit is set.

CM 16 receives the DHCPACK message. It examines the DHCP 66 yiaddr-field126 and chaddr-field 132, and updates its routing table and an ARProuting table to reflect the address pairing at step 320. At step 322,CM 16 sends the DHCPACK message to CPE 18 via CMCI 20 at IP 54 and MAC44 addresses respectively from its routing tables. If the BROADCAST bitin the DHCP 66 flags-field 122 is set to one, CM 16 sends the downstreampacket to a broadcast IP 54 address (e.g., 255.255.255.255), instead ofthe address specified in DHCP 66 yiaddr-field 126. CM 16 uses the MAC 44address specified in DHCP 66 chaddr-field 132 even if the BROADCAST bitis set to located CPE 18. At step 324, CPE 18 receives the DHCPACK fromCM 16 and has established a virtual connection to data network 28.

In the event that CPE 18 is not compatible with the configurationreceived in the DHCPACK message, CPE 18 may generate a DHCP 66 decline("DHCPDECLINE") message and send it to CM 16. CM 16 will transmit theDHCPDECLINE message up the PPP 50 link via PSTN 22 to TRAC 24. On seeinga DHCPDECLINE message TRAC 24 sends a unicast copy of the message toCMTS 12. CM 16 and CMTS 12 examine the DHCP 66 yiaddr-field 126 andgiaddr-field 130, and update their routing and ARP tables to flush anyinvalid pairings.

Upon completion of methods 266 and 292, CM 16 CMTS 12 have valid IP/MACaddress pairings in their routing and ARP tables. These tables store thesame set of IP 54 addresses, but does not associate them with the sameMAC 44 addresses. This is because CMTS 12 resolves all CPE 18 IP 54addresses to the MAC 44 address of a corresponding CM 16. The CMs 16, onother hand, are able to address the respective MAC 44 addresses of theirCPEs 18. This also allows DHCP 66 clients associated with CPE 18 tofunction normally since the addressing that is done in CM 16 and CMTS 12is transparent to CPE 18 hosts.

FIG. 17 is a block diagram illustrating a message flow 326 for methods268 and 294 in FIGS. 15A, 15B, and 16A and 16B. Message flow 326illustrates a message flow for methods 268 and 294, for adata-over-cable system with and without telephony return. In anotherembodiment of the present invention, CM 16 forwards requests from CPE 18via an upstream connection on cable network 14 to DHCP servers 160associated with one or more network host interfaces available on CMTS12.

Method 268 and 294 accomplishes resolving addresses for networkinterface hosts from customer premise equipment in a data-over-cablewith or without telephony return without extensions to the existing DHCPprotocol. Methods 268 and 294 of the present invention are used indata-over-cable system 10 with telephony return. However, the presentinvention is not limited to data-over-cable system 10 with telephonyreturn and can be used in data-over-cable system 10 without telephonyreturn by using an upstream cable channel instead of an upstreamtelephony channel.

Cable Modem Initialization Using Dynamic Protocol Servers

Using the initialization sequences described above (FIG. 12), CM 16obtains configuration parameters at the beginning of every session ondata-over-cable system 10. CM 16 uses an IP 54 address and aconfiguration file name obtained in a DHCP 66 response message duringinitialization to connect to data-over-cable system 10. CM 16 initiatesa TFTP 64 exchange to request the configuration file obtained in theDHCP 66 response message. The configuration file name obtained by CM 16includes required configuration parameters and is a common defaultconfiguration file used by all cable modems for initialization. However,it is desirable to allow an individual cable modern to obtain aconfiguration file different from the default configuration file nameobtained from DHCP server 160 during initialization.

FIG. 18 is a block diagram illustrating data-over-cable system 330 usedfor an illustrative embodiment of the present invention. Data-over-cablesystem is similar to the data over cable system illustrated in FIG. 8.However, FIG. 18 illustrates TFTP 64 server 332 used to obtainconfiguration information 334 in a configuration file for CM 16.

FIG. 19 is a flow diagram illustrating a method 336 for obtaining aconfiguration file different from a requested default configurationfile. At step 338, a first message is received on a first protocolserver from a network device including a request for a firstconfiguration file to configure the network device, wherein the name forthe first configuration file was obtained by the network device from asecond protocol server using a second protocol during an initializationsequence. An identity for the network device is determined using one ormore fields from the first message at step 340. At step 342, a secondconfiguration file is constructed with multiple configuration parametersbased on a determined identity for the network device. The multipleconfiguration parameters include, required configuration parameters, andany of optional configuration parameters or vendor specificconfiguration parameters. At step 344, the second configuration file istransferred to the network device from the first protocol server using afirst protocol in response to the request for the first configurationfile in the first message. The second configuration file, whose contentsare different than the requested first configuration file, is sent tothe network device even though the network device requested the firstconfiguration file. The network device receives a configuration filedifferent from a default configuration file requested by the firstnetwork device and constructed specifically for the network device.

FIG. 20 is a block diagram illustrating a method 350 for obtaining aconfiguration file for a cable modem for an illustrative embodiment ofthe present invention. At step 352, TFTP server 332 receives a TFTP 64Read-ReQuest ("RRQ") message from CM 16 in data-over-cable system 330.The TFTP 64 read request is sent from CM 16 to TFTP server 332 via TRAC24 and PSTN 22 on an upstream telephony connection. In anotherembodiment of the present invention, the TFTP 64 RRQ message is sent toTFTP server 332 via cable network 14 and CMTS 12 on an upstream cabletelevision connection. The TFTP RRQ message includes one or more headersillustrated in Table 10. For more information on TFTP 64 headers, seeRFC-1350.

                  TABLE 10                                                        ______________________________________                                         ##STR1##                                                                     ______________________________________                                    

The local medium header allows a TFTP 64 message to be transported on alocal medium (e.g., cable network 14 or PSTN 22). The IP 54 header andUDP 60 header allow TFTP 64 to be transported with UDP/IP. TFTP 64 usesan IP 54 address from the IP 54 header. A source and destination portfield in the UDP 60 header are used by TFTP 64 and the UDP 60 lengthfield reflects the size of the TFTP 64 packet. Transfer IDentifiers("TIDs") are used by TFTP 64 and are passed to UDP 60 for use as ports.A TFTP 64 message header is illustrated in Table 11.

                  TABLE 11                                                        ______________________________________                                         ##STR2##                                                                     ______________________________________                                    

TFTP 64 RRQ message field includes a field (i.e., filename) for adefault configuration file sent by a DHCP server 160 during aninitialization sequence (FIG. 12) to CM 16. The filename for the defaultconfiguration file is sent to CM 16 in boot-file-name field 136 (FIG. 6)in a DHCPACK message during initialization.

Returning to FIG. 20 at step 354, TFTP server 332 extracts an IP 54address (e.g., 124.35.14.58) for CM 16 from the IP 54 header in the TFTP64 RRQ message. TFTP server 332 performs a reverse look-up on CM's 16 IP54 address through a Domain Name System ("DNS") using reverse DNS namespace, also called "in-addr.arpa" name space. Reverse DNS mapping, mapsthe address 124.35.14.58 back to a domain name for the cable modem(e.g., "cm-type1.data-over-cable.net"). As is known in the art, DNS isan application protocol used to map symbolic names (e.g.,data-over-cable.net) to a network address such as an Internet address(e.g., 124.35.14.58). For more information on DNS see RFC-882, RFC-883and RFC-1033 incorporated herein by reference. A domain name entry usedfor reverse DNS mapping of IP address 124.35.14.58 is"58.14.35.124.in-addr-arpa." An IP 54 address is written in reverseorder for reverse DNS mapping. Table 12 illustrates pseudo-code for anexemplary file of DNS resource types available to TFTP server 332 forforward and reverse DNS mapping. However, other resource types and filelayouts could also be used.

                  TABLE 12                                                        ______________________________________                                        ;cable modem hosts entries                                                    cm-type1   A       124.35.14.58                                                          A       124.35.14.59                                                          ...                                                                           HINFO   3Com Cable Modem                                           cm-type2   A       124.35.14.60                                                          A       123.35.14.73                                                          ...                                                                           HINFO   U.S. Robotics Cable Modem                                  ;reverse DNS entries                                                          58.14.35.124.in-addr.arpa                                                                    PTR     cm-type1.data-over-cable.net                           59.14.35.124.in-addr.arpa                                                                    PTR     cm-type1.data-over-cable.net                           60.14.35.124.in-addr.arpa                                                                    PTR     cm-type2.data-over-cable.net                           73.14.34.124.in-addr.arpa                                                                    PTR     cm-type2.data-over.cable.net                           ______________________________________                                    

As is illustrated in Table 12, CM 16 of a first type is assignedInternet Addresses (designated by the "A," in Table 12) by DHCP 66server 160 of 124.35.14.58 or 124.35.14.59. Only two Internet addressesare shown for cable modems of a first and a second cable modem type.However, the invention is not limited to two cable modem types, twoInternet addresses, or sequential Internet addresses for each cablemodem type. CM 16 of includes type-1 Host INFOrmation ("HINFO")describing the first type of cable modem as a cable modem from the 3ComCorporation of Santa Clara, Calif. Table 12 contains similar entries fora second type of cable modem by U.S. Robotics Corporation of Skokie,Ill.

When TFTP server 332 extracts an IP 54 address from the IP 54 header ofthe TFTP 64 RRQ message, it performs a reverse DNS mapping process usinginformation from a table such as that illustrated in Table 12. The IP 54address 124.35.14.58 is used in the reverse DNS format (e.g.,58.14.35.124.in-addr.arpa). As is illustrated in Table 12,58.14.35.124.in-addr.arpa maps with a pointer (i.e., PTR) to the domainname "cm-type1 .data-over-cable.net." The prefix of the domain name"cm-type1" has the table entries for a cable modem of a first type(i.e., a 3Com cable modem). In one embodiment of the present invention,The HINFO field for the cable modem entries is used to determine thetype of cable modem assigned to the IP 54 address extracted in the TFTP64 RRQ message.

Returning again to FIG. 20, at step 356 a second configuration file isconstructed with multiple configuration parameters based on a determinedidentity for CM 16. CM 16 specific configuration data is constructed ina file that is downloaded to CM 16 via TFTP 64. The second configurationfile is a file in the same format defined for DHCP 66 vendor extensiondata. The file comprises a of a number of configuration parameters eachin TLV form (i.e., Type/Length/Value), where Type is a single-octetidentifier which defines a parameter, Length is a single octetcontaining the length of the value field in octets (not including typeand length fields) and Value is from one to 254 octets containing aspecific value for the parameter. Table 13 illustrates the configurationparameters that can be included in the second configuration file.However, more of fewer configuration parameters can also be used.

                  TABLE 13                                                        ______________________________________                                        The following configuration parameters are supported by all CMs 16 and        included in the second configuration file:                                    • Network Access Configuration parameter.                               • End Configuration parameter.                                          The following configuration parameters may be included in the second          configuration file:                                                           • Downstream Frequency Configuration parameters.                        • Upstream Channel ID Configuration parameters.                         • Class of Service Configuration parameter.                             • Vendor ID Configuration parameter.                                    • Baseline Privacy Configuration parameter.                             • Software Upgrade Filename Configuration parameter.                    • SNMP 62 Write-Access Control                                          • SNMP 62 MIB Object                                                    • Pad Configuration parameter.                                          The following configuration parameters may be included in the second          configuration file:                                                           • Vendor Specific Configuration parameters.                             ______________________________________                                    

The configuration parameters follow each other directly in theconfiguration file, as a stream of octets. Configuration parameters aredivided into three types: (1) Required standard configuration parametersthat are required for all cable modems; (2) Optional standardconfiguration parameters that are not required for all cable modems; and(3) Vendor-specific configuration parameters.

Exemplary configuration parameters are illustrated in TLV format inTable 14. However, more or fewer configuration parameters could also beused. In addition, only a description of the Value in the TLV format isincluded since the numbers used for the Value fields are implementationspecific.

                  TABLE 14                                                        ______________________________________                                        Type    Length       Description of Value                                     ______________________________________                                         1      4            Receive frequency                                         2      1            Upstream channel identifier                               4x     N            Class of service header                                   41     1            Class identifier                                          42     4            Maximum downstream data                                                       rate in bits/sec                                          43     4            Maximum upstream data rate                                                    in bits/sec                                               44     1            Upstream channel priority                                 45     4            Upstream guaranteed                                                           minimum data rate in bits/sec                             46     2            Maximum upstream                                                              configuration setting in                                                      minislots                                                 47     1            Privacy enable                                            8      3            Vendor Identifier configuration                                               setting                                                   17x    N            Baseline privacy settings                                                     header                                                   171     4            Authorize timeout seconds                                172     4            Reauthorize wait timeout                                                      seconds                                                  173     4            Authorization wait timeout                                                    seconds                                                  174     4            Operational wait timeout                                                      seconds                                                  175     4            Re-key wait timeout seconds                              176     4            TEK grace time seconds                                    9      N            Software upgrade filename                                 10     1            SNMP 62 access control                                    11     N            Arbitrary SNMP 62 object                                                      setting                                                   0      N            Padding to align on 4-byte                                                    boundary                                                  3      1            Network access                                            6      16           CM-MIC                                                    7      16           CMTS-MIC                                                 255     N/A          End-of-file                                              ______________________________________                                    

Authentication of the configuration information is provided by twoMessage Integrity Check ("MIC") fields, "CM-MIC" and "CMTS-MIC". TheCM-MIC is a cryptographic digest created with a cryptographic hashingfunction that ensures data sent from TFTP server 332 is not modifieden-CM-MIC route. CM-MIC is not an authenticated digest (i.e., it doesnot include any shared secret password). The CMTS-MIC is also acryptographic digest used to authenticate configuration information sentto CMTS 12 during registration.

In an illustrative embodiment of the present invention, Message Digest 5("MD5") cryptographic hashing function is used to create the CM-MIC andCMTS-MIC digests as described in RFC-2104 incorporated herein byreference. However, other cryptographic hashing functions could also beused. As is known in the cryptography arts, MD5 is a secure, one-wayhashing function used to create a secure hashing value that is used toauthenticate messages.

The second configuration file, has the same structure as the first ordefault configuration file structure. However, the second configurationfile structure contains different configuration information than therequested first configuration file.

FIG. 21 is a block diagram illustrating a second configuration fileformat 360 used to configure CM 16 with configuration parameters basedon a determined identity for CM 16. Configuration file at 360 includesmultiple configuration settings config-1 362, config-2 364, . . . ,config-N 366 (only three of which are illustrated), a CM-MIC field 368and a CMTS-MIC field 370. Table 15 illustrates a method for creation ofthe second configuration file. However, other methods could also beused.

                  TABLE 15                                                        ______________________________________                                        Create the TLV entries (e.g., 362, 364, ... , 366) for all parameters         used by                                                                       CM 16.                                                                        Calculate CM-MIC field 368 by performing an MD5 digest over the bytes         of the TLV entries.                                                           Add CM-MIC field 368 to the file following the last TLV entry.                Calculate CMTS-MIC field 370 using the method illustrated in Table 16.        Add CMTS-MIC field 370 to the file following CM-MIC field 368.                Add an End-of-File ("EOF") marker to the file.                                ______________________________________                                    

Table 16 illustrates a method for calculating CMTS MIC field 360 fromstep 4 in Table 15.

                  TABLE 16                                                        ______________________________________                                        CMTS-MIC field 370 is calculated by performing an MD5 digest over the         following configuration parameter fields, when present in the                 configuration file, in the order shown:                                       • Downstream Frequency Conflguration parameter.                         • Upstream Channel ID Configuration parameter                           • Network Access Configuration parameter.                               • Class of Service Configuration parameter.                             • Vendor ID Configuration parameter.                                    • Baseline Privacy Configuration parameter.                             • Vendor specific Configuration parameters.                             • CM-MIC 368 value                                                      • Authentication string                                                 The configuration parameter fields are treated as if they were                contiguous                                                                    data when calculating the MD5 digest.                                         ______________________________________                                    

Returning again to FIG. 20, at step 358 TFTP server 332 transfers thesecond configuration file to CM 16 using TFTP 64. The secondconfiguration file is sent to CM 16 on a downstream cable connection viaCMTS 12 and cable network 14. After receiving the second configurationfile, CM 16 validates the second configuration file by checking CM-MICfield 368 and CMTS-MIC field 370. In another embodiment of the presentinvention CM 16 validates the second configuration file by checkingCM-MIC field 368 or CMTS-MIC field 370. If the data in the secondconfiguration file is valid, CM 16 uses configuration information in thesecond file to continue its initialization.

With method 350, CM 16 receives a second configuration file from TFTPserver 332 different from the default configuration file whose name issupplied by a DCHP server 160 during initialization and the filerequested by CM 16 at step 352. Method 350 provides flexibility forinitializing a CM 16 in data-over-cable system 10 without modifying anyDHCP server 160 in data-over-cable system 330.

FIG. 22 is a block diagram illustrating another method 372 for obtaininga configuration file for a cable modem in another embodiment of thepresent invention. Method 372 allows configuration information for CM 16to be obtained and transferred "on-the-fly" as a stream of octetswithout actually creating a second configuration file. Steps 374 and 376are similar to steps 352 and 354 of method 336 illustrated in FIG. 20.

However, at step 378, configuration information based on the determinedidentity of CM 16 is obtained and transferred as a stream of octets withTFTP 64 on-the-fly to CM 16 without creating a second configurationfile. The configuration information is encoded in TLV format as wasdescribed above. In one embodiment of the present invention,configuration information as multiple confrontation parameters is storedin an internal data structure in TFTP server 332 that includes a layoutsimilar to FIG. 21, and CM-MIC 368 and CMTS-MIC 370 are calculated asdescribed in Tables 15 and 16 using the internal data structure. An endof file marker is sent after CMTS-MIC 370 is sent.

In another embodiment of the present invention, configurationinformation is sent on-the-fly without storing the information in aninternal data structure. In such an embodiment, CM-MIC 368 is calculatedon-the-fly as configuration information is sent. A preliminary CMTS-MIC370 is calculated as configuration information is sent, and a finalCMTS-MIC 370 is calculated after CM-MIC 368 is calculated and sent. Inyet another embodiment of the present invention, CM-MIC 368 and CMMIC-370 are not calculated or sent with the configuration informationand other methods are used to validate the configuration informationsent by TFTP server 32 (e.g., sending encrypted TFTP 64 packets (e.g.,RSA encryption), using a Secure Sockets Layer ("SSL") to transfer TFTP64 packets or another other cryptographic process).

Method 372 is used in place of method 350 when CM 16 has only a smallnumber of configuration parameters that are used to configure CM 16.Method 372 allows CM 16 to be initialized slightly faster that method350 if the number of configuration parameters for CM is small.

In an illustrative embodiment of the present invention, TFTP server 332is called a "dynamic TFTP server" since configuration information for CM16 is constructed based on a IP 54 address in use for CM 16 and TFTPserver's 332 determination of the identity of a network device such asCM 16. Using method 336, 350 and/or method 372 in a dynamic TFTP 64server allows a cable modem to obtain configuration informationdifferent from a default configuration file whose name is supplied byDCHP server 160 in a DCHPACK message during cable modem initialization.An illustrative embodiment of the present invention provides moreflexibility and control of a cable modem in a data-over-cable system. Itcan be used without modifying any DCHP server in the data-over-cablesystem the present invention can be used in a data-over-cable systemwith telephony return or in a data-over-cable system without telephonyreturn.

It should be understood that the programs, processes, methods, systemsand apparatus described herein are not related or limited to anyparticular type of computer apparatus (hardware or software), unlessindicated otherwise. Various types of general purpose or specializedcomputer apparatus may be used with or perform operations in accordancewith the teachings described herein.

In view of the wide variety of embodiments to which the principles ofthe invention can be applied, it should be understood that theillustrated embodiments are exemplary only, and should not be taken aslimiting the scope of the present invention. For example, the steps ofthe flow diagrams may be taken in sequences other than those described,and more or fewer elements or component may be used in the blockdiagrams.

The claims should not be read as limited to the described order orelements unless stated to that effect. In addition, use of the term"means" in any claim is intended to invoke 35 U.S.C. §112, paragraph 6,and any claim without the word "means" is not so intended. Therefore,all embodiments that come within the scope and spirit of the followingclaims and equivalents thereto are claimed as the invention.

I claim:
 1. In a data-over-cable system including a plurality of networkdevices, a method of initializing a network device, the methodcomprising the following steps:receiving a first message on a firstprotocol server with a first protocol from a network device including arequest for a first configuration file to configure the network device,wherein the name for the first configuration file was obtained by thenetwork device from a second protocol server using a second protocolduring an initialization sequence; determining an identity for thenetwork device by performing a reverse Domain Name System lookup on anetwork address from the first message, wherein the identity includes adevice type for the network device; constructing a second configurationfile with a plurality of configuration parameters based on a determinedidentity for the network device; and transferring the secondconfiguration file to the network device from the first protocol serverusing the first protocol in response to the request in the first messagefor the first configuration file, thereby providing a secondconfiguration file specifically for the network device and differentfrom the requested first configuration file.
 2. A computer readablemedium having stored therein instructions for causing a centralprocessing unit to execute the steps of the method of claim
 1. 3. Themethod of claim 1 wherein the first protocol server is a Trivial FileTransfer Protocol server and the second protocol server is a DynamicHost Configuration Protocol server.
 4. The method of claim 1 wherein theTrivial File Transfer Protocol server is a dynamic Trivial File TransferProtocol server.
 5. The method of claim 1 wherein the first protocol isa Trivial File Transfer Protocol and the second protocol is a DynamicHost Configuration Protocol.
 6. The method of claim 1 wherein thenetwork device is a cable modem.
 7. The method of claim 1 wherein thestep of determining an identity for the network device includesdetermining a device type for the network device by performing a reverseDomain Name System lookup using an Internet Protocol address from aheader field in the first message from the network device.
 8. The methodof claim 1 wherein the step of constructing a second configuration filewith a plurality of configuration parameters based on a determinedidentity for the network device includes constructing the secondconfiguration file with required standard configuration parameters, andany of optional standard configuration parameters, or vendor-specificconfiguration parameters.
 9. The method of claim 8 wherein the requiredstandard configuration parameters, optional standard configurationparameters and vendor-specific configuration parameters in the secondconfiguration file are encoded in a type-length-value encoding formatincluding two or more message integrity check values used forauthentication.
 10. The method of claim 1 wherein the secondconfiguration file includes one or more message integrity check valuesto verify the integrity of the configuration parameters.
 11. The methodof claim 1 wherein the second configuration file includes one or moreconfiguration parameters not included in the requested firstconfiguration file.
 12. In a data-over-cable system including aplurality of network devices, a method of initializing a network device,the method comprising the following steps:receiving a first message witha first protocol on a first protocol server from a network deviceincluding a request for a first configuration file to configure thenetwork device, wherein the name for the first configuration file wasobtained by the network device from a second protocol server using asecond protocol during an initialization sequence; determining anidentity for the network device by performing a Reverse Domain Namesystem lookup on a network address from the first message, wherein theidentity includes a device type for the network device; and transferringconfiguration information dynamically as a data stream to the networkdevice in a pre-determined format based on a determined identity for thenetwork device using the first protocol, wherein the configurationinformation is dynamically sent as a data stream in response to therequest in the first message for the first configuration file andwherein the configuration information sent dynamically as a data systemis different form configuration information in the first configurationfile.
 13. A computer readable medium having stored therein instructionsfor causing a central processing unit to execute the steps of the methodof claim
 12. 14. The method of claim 12 wherein the step of determiningan identity for the network device includes determining a device typefor the network device by performing a reverse Domain Name System lookupon an Internet Protocol address from a header field in the first messagefrom the network device.
 15. The method of claim 12 wherein the step oftransferring configuration information dynamically as a data stream tothe network device in a pre-determined format based on a determinedidentity for the network device includes transferring required standardconfiguration parameters and any of optional standard configurationparameters or vendor-specific configuration parameters encoded in atype-length-value encoding format including two or more messageintegrity check values used for authentication.
 16. The method of claim12 wherein the first protocol server is a dynamic Trivial File TransferProtocol server.
 17. A dynamic protocol server for transferringconfiguration information for a network device in a data-over-cablesystem, the dynamic protocol server comprising in combination:aplurality of network device type identifiers, for identifying aplurality of network device types, wherein a network device identity isobtained by performing a reverse Domain Name System look-up on a networkaddress in a protocol message sent to the dynamic protocol server by anetwork device requesting a first configuration file, wherein theplurality of network device type identifiers include device types for aplurality of network devices; and a plurality of configurationinformation constructors, for dynamically constructing configurationinformation for initializing a network device based on a device typedetermined by a network device type identifier, wherein configurationinformation is constructed from the plurality of configurationinformation constructors based on a determined network device identityfor a network device, thereby providing a second configuration filespecifically for the network device and different from a firstconfiguration file originally requested by the network device.
 18. Thedynamic protocol server of claim 17 wherein the dynamic protocol serveris a dynamic Trivial File Transfer Protocol server and the dynamicTrivial File Transfer Protocol server sends a network device a secondconfiguration file or configuration information as a dynamic data streamthat is constructed based on a determined identify for the networkdevice instead of a first configuration file requested by the networkdevice.
 19. The dynamic protocol server of claim 17 wherein theplurality of network device identifiers determine a device type for acable modem by performing a reverse Domain Name System lookup on anInternet Protocol address from a header field in a Trivial File TransferProtocol message.
 20. The dynamic protocol server of claim 17 whereinthe plurality of configuration information constructors include requiredstandard configuration parameters, and any of optional standardconfiguration parameters or vendor-specific configuration parameters forinitializing a cable modem.
 21. In a data-over-cable system including aplurality of cable modems, a method of initializing a cable modem, themethod comprising the following steps:receiving a first Trivial FileTransfer Protocol message on a dynamic Trivial File Transfer Protocolserver from a cable modem including a request for a first configurationfile to configure the cable modem, wherein the name for the firstconfiguration file was obtained by the cable modem from a Dynamic HostConfiguration Protocol server using a Dynamic Host ConfigurationProtocol during an initialization sequence; determining an identity forthe cable modem by performing a reverse Domain Name System lookup on theInternet Protocol address for the cable modem from the first TrivialFile Transfer Protocol message, wherein the identity includes a devicetype for the cable modem; constructing a second configuration file witha plurality of configuration parameters based on a determined identityfor the cable modem; and transferring the second configuration file tothe cable modem from the dynamic Trivial File Protocol server using theTrivial File Protocol in response to the request in the first TrivialFile Protocol message for the first configuration file, therebyproviding a second configuration file different from the requested firstconfiguration file and specifically for the determined identity of thecable modem.
 22. A computer readable medium having stored thereininstructions for causing a central processing unit to execute the methodof claim 21.